On a more serious note, what does it matter how it's done?
It matters. I would make it believable if possible
You kill the Reapers by shooting a tube,
I do have a problem with shooting the tube. I like to hear from Bioware why I couldn't shoot the tube from a distance. Of course I like to give them a handgun and tell them to shoot a container full of explosives so it will explode. I doubt they would do that. I'm sure they would want to shoot at it from a distance.
or upload your brain pattern into them by grabbing a pair of electrodes, or rewrite everyone's DNA by leaping into a beam of space magic.
I won't comment on these two since I don't care about them especially the green stuff
Is how a conventional victory is achieved really important when compared to that?
If conventional victory was possible, you might complain since you have posted that its not possible with the numbers they have. And if you didn't complain about that, you might complain about the way a conventional victory was achieved. You might want a victory to happen this way or that way.
Maybe it's by raw EMS. High enough number and enough Reapers are destroyed where galactic civilization can continue, though the Reapers remain a recurring threat for centuries to come.
Why would the reapers retreat if they lost x number?
The ems was a joke. A player can head to Earth with 3100 ems and get the same results as a player heading to Earth with 10 000 ems. Since 3100 is needed for the breath scene, what is the other 6900 ems doing? The game gives no incentive to get more war assets.
If a player is able to get peace between the geth and quarians, how many ships are seen coming through the relay heading to Earth? I don't know if anyone has counted or if there has been a number posted for how many. I'll just use the number 1000 for the heck of it. I have read a post that someone counted about 100 reapers over Earth. So the organics have the reapers outnumbered 10 to 1. You would think it would be a mismatch.
The problem with that is all those ships are bunched together. Spread them out. The other thing is to have each ship assigned to firing on a reaper instead of just firing at whatever. There's no way all those reapers would've been destroyed, but a lot would've been. The other thing is, once they start taking losses, they can call for reinforcements. We can't since all the fleets are at Earth. We would lose.
Or there could have been a secondary plot through ME3 of breakthroughs in weapons. More powerful thanix weapons. Directed energy weapons. Nukes. Fulfill certain side missions and Sword and Shield will have weapons the Reapers have no defense against, evening the fight. (I'd hesitate to call this "conventional" though
Not sure what nukes could do against the reapers since we're not given the opportunity to use them.
Or Heck, Jeff Goldblum and Will smith fly into the Citadel and upload a virus from an omnitool that drops the Reapers' kinetic barriers
I've posted a few times before. No one knows exactly what the crucible will do. Once the arms to the citadel are completely opened, the crucible fires some kind of pulse that reprograms the reapers. They stop the harvest and are seen leaving the galaxy. Yes this does require the use of the crucible and its not a conventional victory, but it does get rid of everything after Shepard passes out.
while Randy Quaid flies a missile-laden gunship into Harbinger.
I wouldn't make it that easy. The game can be setup to where destroying Harbinger would cause the other reapers to stop and leave the galaxy. I believe it would be harder to destroy Harbinger than getting the crucible attached to the Citadel
Another way is after the thing tells Shepard that it controls the reapers, Shepard tells Hackett to destroy the citadel. Will that be enough to stop the reapers? Only one way to find out. But that option is not available.
is that really more nonsensical than Synthesis?
I won't comment on the green stuff. I will just say I'm not a fan of it
For a conventional victory to happen, you need to have leaders that know what they're doing when attacking the reapers. It will also take a very long time to get that victory. The more losses the organics take, the longer the war will take. Its possible a victory would happen after Shepard dies of old age.
I have posted that if the reapers had only 300 capital ships plus destroyers, troop transport ships and processing ships, they would beat us easily. All they have to do is enter a system, shutoff the relay. It cuts off any reinforcements. The reapers destroy the military in that system. They repeat this for each system then start harvesting.
If those same 300 did not shutoff the relay and spread themselves all over the galaxy, then yes, I would agree a conventional victory can happen. It all depends on who is leading the attacks and how those attacks are done.
Its up to Bioware to decide how many reapers there are. Here's a post with the possible number they may have at the start of this cycle