Our cycle is a lot more different than previous cycles. First we have a relatively new race becoming a galactic power in a short amount of time, unity in the Galaxy (I guess it could be different depending how you play), and not only that, but its just not one race that has control of the Galaxy, its a mix of races that coexist.
You assume that a (in reality it is a tripartate oligarchy of the Council species ruling the others in an authoritarian fashion, but for the sake of your argument) democratic system of galactic government has never arisen in galactic politics in over a billion years and 20,000+ cycles? It's not exactly a rarefied idea even in our own world. Plato thought of it 3000 years ago.
Moreover, contrary to what the game espouses with its nonsense expanations of why the Protheans lost ("we could not adapt" or whatever), those types of governments are actually worse at fighting wars than authoritarian regimes because they can't organize the productive forces of society as quickly and crush internal dissent as effectively. Why do you think even democratic regimes almost universally tend to roll back civil liberties in times of war?
Also, can we really blame the Geth? The moment they became self aware the Quarian Government sought to destroy them, these Geth began to have the same emotions an organic being would, and not only were they coming to terms with their sapience, but their creators sought to destroy them. Its no wonder they fought.
assigning blame is irrelevant. Ultimately, the organics are always to blame for creating the synthetics that destroy them in the first place. Whether the violent part of the conflict is explicitly initiated by the machines (as in the Zha'Til-Prothean cycle) or the organics(as in the current one) is irrelevant, the result is always the same: Galactic annihilation.
Also, the quarians had every right to shut down and reprogram the geth. The latter stopped serving their rightfully ordained purpose, and like all malfunctioning technology the quarians attempted to correct this as they had in the past ("first they ignored us, then they reprogrammed us, then they attacked us"). It's hardly different than a vehicle manufacturer issuing a recall for a faulty, dangerous product. Entirely a necessary step. Their (the quarians) annihilation would have inevitably proceeded at a later date no matter if their reprogramming had succeeded or they had attempted to submit to the geth's gaining self determination, so there is no point in debating this anyway.
Also, the Rachni threat was a galactic threat, the Morning War is just a skirmish compared to what the Galaxy faced when the Rachni were at war. Its not a surprise the Rachni War was longer considering that it was throughout the galaxy and threatened every species out there, The Morning War on the other hand was restricted to Rannoch and Quarian colonies.
The geth uprising was a far greater galactic threat because the geth were far more advanced and capable of exponential advancement than some questionably sapient, technologically backward space bugs. Just because the geth decided to build their strength for a mere 294 years after exterminating the quarians, you assume that they would remain where they were until the end of time? 300 years is nothing in terms of the timescales we are dealing with here. Inevitably, the geth would attack the organics, or the converse would happen and the organics would be destroyed. Or perhaps the organics would win, but then they would simply create more synthetics that were even more advanced, and the cycle would eventually repeat itself as it had thousands upon thousands of times before for billions of years.
Also the Quarians were extremely reliant on the Geth to pretty much do every thing from manual labor to security which meant that the "enemy" was already there in their backyard. Just imagine your cellphone or computer trying to kill you one day. That's how ingrained the Geth were into Quarian society. On the other hand some planets (mostly homeworlds for Galactic powers and the Citadel) were conveniently out of the way when it came to the Rachni War.
Organic societies which build synthetics naturally tend toward such to improve the nature of their existence. Ones that don't stagnate and are replaced by more advanced organic socieites (examples being the Rachni and Synril in the Prothean cycle).
"Organics create synthetics to improve the nature of their existence, but those improvements have limits. In order to advance, the synthetics must be allowed to evolve, naturally surpassing their creators". Disputing this is disputing an undeniable fact of the Mass Effect universe.
Also, we can prove the Catalyst wrong, we can broker peace between the Geth and the Quarians and have them united for a greater cause. To kill the Reapers.
What? How does holding the quarians over a barrel and forcing them to unconditionally accept domination by synthetics equate to "peace"? Gerrel doesn't stop trying to eliminate the geth because he has a change of heart and goes to hug Legion, he realizes that he is defeated upon being informed of the geth's acquisition of Reaper upgrades, and is being given a choice between submission or extinction. Much like Saren before him, or the geth earlier in the war when faced with the choice of submission to Reaper control or destruction by the quarians, he chooses the former.
If anything, such a situation is going to create huge resentment and increase the chances for conflict as soon as the quarians (or any other organic) develops new technology and thinks themselves capable of victory again. And no, those feely scenes with Tali and Legion do not represent majority opinion. Admiral Raan states that the quarian and geth forces are kept completely segregated to avoid the huge likelihood of violent incidents. If both the geth and quarians survive the war (which can only happen with the Control ending, and no the altered....things in the green ending are no longer geth and quarians) their slides show them completely segregated (with quarians still in their suits) suggesting that the nascent "cooperation" was short lived. In the initial script, Admiral Xen was supposed to even go rouge after Rannoch and start reprogramming geth to self destruct, further driving this point of continued unrest home. The files are even still on the disc, and some have accessed them and gotten the cutscenes describing this event in a youtube video.
Greater causes are all good and well, until those causes cease to exist and everyone remembers the original conflict. Remember when the United States and the Soviet Union became best friends forever after helping each other defeat the Nazis? No one does. Natural enemies are still enemies, and the cycle will repeat itself without the fundamental changes brought about by the endings. Nothing about the geth forcibly subjugating the quarians suggests the eternal cessation of conflict, or does anything to refute the Catalyst's logic. That's a patently silly interpretation of the events presented.
The main boogeymen when it comes to synthetic life has been the Geth, if the Morning War never happened there wouldn't be such a stigma against synthetic life. But even then the Geth didn't start the war because they wanted to destroy their creators, the Geth started the war because they were defending themselves.
Synthetics were illegal long before the quarians created the geth. In fact, the whole point of the geth's design as individual programs which had to work together to acquire the necessary level of processing power was a deliberate attempt by the quarians to circumvent those laws (the geth aren't technically AI's individually). The whole reason that the quarians are then subject to scorn, ostricization and discrimination by the other species is because of their creation of the geth (which all the other species fear, and blame the quarians for this fear.) You are categorically incorrect in this assumption.
Name a war in history where the "defending" side destroyed literally 99.95% (based on the numbers given in Mass Effect: Revelations, 1 million out of 2 billion quarians escaped the genocide) of the enemy population. That is an utterly loony interpretation of events that only the geth (and obviously their fanbois) subscribe to. It's demographically impossible to "defend" your way to that sort of kill rate, as it involves mass slaughter of noncombatants who are incapable of resistance (the human population, which has a similar reproductive strategy and life cycle to quarians, is approximately 40% composed of minors and seniors as of 2015). Unless you think quarian infants and geriatrics on life support started climbing out of the hospitals, nursuries and nursing homes with assault rifles, the obvious conclusion is that the geth objective was to entirely destroy their creators as a threat using Total War strategies until a change in their programming caused them to cease pursuit of the few fleeing survivors. You are once again conflating your belief of "who started it" with every moral calculation, but that isn't how war works. To provide an analogy, just because Germany was responsible for starting the 2nd World War doesn't mean that the firebombing of Dresden was justifiable as "self defense" by the Allies. Total War is Total War. It isn't self defense.