The Mad Hanar wrote...
I'm willing to listen if you're willing to look at the evidence that it's extremely unlikely...
-It took a good chunk of the Alliance fleet to take down Sovereign, while he wasn't fighting back
-It took a good chunk of the Quarian fleet to take down the Rannoch Reaper, while he wasn't fighting back
-It took the galaxy's biggest Thresher Maw and a good amount of luck to take down the Tuchanka Reaper, and it was a small one.
-The galaxy's best military, the Turians, were being decimated, so much so that Palaven had to be fully evacuated.
-Hammer was being overrun on Earth. It would also take just a few Reapers to decimate the ground forces, really.
-The Migrant Fleet is made up of mostly civilian ships
-The Alliance Fleet was weakened during the Sovereign/Geth attack
-It's been said or implied many times that the Salarians and Asari aren't built for conventional war.
-The Reaper force at Earth wasn't the entire Reaper force, and they were still winning.
-It takes one Reaper to take out 10 of our ships and it takes ten of our ships to take out a Reaper...
Well guys?
I'm going to TRY and respond to this as best I can, I'm very tired. And eloquence and major discussion is not really up there for me when I should probably be sleeping. But I'll humor you since I've seen you around and I don't think your a bad guy.
1. The Alliance fleet that took on Sovereign was unprepared in any fashion to deal with what they were facing. They were equipped for fighting with the other races. Its the Gundam Wing effect. In short, the regular Mechs seemed weak and pathetic because they were built and equipped to fight each other which they were perfectly fine for. But against 5 war machines that were designed to conquer a PLANET, they fell short and made those 5 war machines look invincible though they were not. But by the time of ME3, this problem has been solved by equipping said ships with the enemies own weaponry.
2. The Rannoch Reaper, really, I personally believe they made it tougher then it appeared for gameplay purposes. Someone probably went "Hey, lets have Shepard fight a REAPER, that will be COOL!" and then everyone went with it. And they figured out how to do it. But like any good video game fight, left logic at the door cause if you pwn the boss in one shot, its no fun. Because really, it shouldn't have taken so many shots from an ENTIRE FLEET to take down a single "small" Reaper when the lore alone states that (I think) 4 dreadnaughts can take out a Sovereign sized Reaper. (Again I think, tired, need to check at some point to confirm)
3. The fact that a really big Thresher Maw smacked around and dragged a "small" Reaper to its death underground doesn't help show how "unstoppable" they are, or that they can't be fought conventionally. It shows that they can be over-powered and bludgeoned to death. And that ships, which dwarf both of them, should be able to over-power them. If anything, its good proof of that.
4. The Turians were caught with their pants down for being stubborn, "Ah yes, Reapers, we have dismissed this claim" rings a familiar bell. Much like most races. Except that they fought back, and held pretty hard. Even though they lost ground. Once they had the Krogans help however, as I recall, they pushed the Reapers back. Doesn't seem like the Reapers are so unstoppable there either. Just really tough.
5.If I recall, they faced a Reaper directly as a ground squad. Every time Shepard himself had to do that. Short of the Rannoch Reaper at the end, he had to avoid that because of the death beams. Ground troops VS Reapers, unless they have something powerful like Cains, not exactly the best of plans.
6. And yet the Migrant fleets actions toasted a Reaper. That's some civilian ships. Oh yes, they have Thanix cannons, don't they?, I remember hearing or reading something while playing that they ordered in and retrofitted them onto all the ships. Civie and dreadnaught alike.
7. Yeah, they lost ships and good men. And as I recall, your actions during ME3 aid in restoring the fleet. But, hey, what does it matter with the way the game is written?
8.Taking a page from real life, the Viet Cong were hardly conventional, and they forced our American troops into such a position that we had to withdraw. Unconventional warfare can be devestating if applied correctly. And of course, written well.
9. Earth got hit hard and fast, somehow taken by surprise. I blame the writing. But in the end, you had Reaper's and their ground forces tromping on earth, and forcing alliance forces to keep falling back. The ships in orbit that didn't get away, clearly destroyed. Pretty much it looks like those who could run, ran. Leaving everyone else behind to fight while Shepard is left to try to save them and the rest of the universe.
10. And the question on my mind is exactly how many Reapers are there really?, it always looked like a few hundred and reaching no greater then a thousand. Assuming 1 Reaper was actually made per cycle.
Now right off the bat, I'm gonna say that, the writing is the real problem. The means to defeat the Reapers are right there, built into the very fabric of Mass Effect universe. The Thanix cannon's are charged particle weapons, CP weapons in fiction are very powerful weapons that work as a two fold attack. An energy attack and a solid physical attack.
Matter is charged with energy and at the same time super heated, and when fired, the energy tears through things like shields, and the matter keeps pounding and melting away at the target until the weapon ceases firing. Not much is able to stand up to these types of weapons.
And in Mass Effect, the Thanix Cannon's fire near the speed of light. That makes them EXTREMELY powerful charged particle weapons.
Reapers have many powerful attributes, that is very true. But their real strength, the so called "Undefeatable" status, comes from their shields. Kinetic Barriers, really strong ones.
We've all seen it, you take out those shields and their bodies are no stronger then any other ship out there. As when Sovereign's shields were taken out, the Normandy only needed two missiles to destroy it. The fleets fire otherwise wasn't hitting Sovereign at the time of its destruction.
And there is no evidence that Harbringer, or any other Reaper is designed any differently then Sovereign on a basic level short of size.
I'd go as far to say that other theories floating around like hitting them with Cain's would work, as that is nuclear devestation focused on specific points. It pretty much one shotted the Reaper Larva, and probably would have if it wasn't a boss/game play mechanic. But to what I was saying, shields in fiction don't do well when you focus alot of damage on one spot.
Furthering my point, the cyclonic shields from ME2, they specifically pointed out in their design that it worked to deflect damages away so they can stand up better for when you go to deal with the Collectors and their juggernaut of a ship. Litterally diverting it away, spreading it out and allowing it to brush off like a reed bending in the wind.
My oldest friend has often said "The tree that stands against the wind will break, The reed that bends with the wind does not snap" and that applies here at least to a degree.
And time and time again in the lore it pops up that certain things should be able to do certain things. Like that Volus bomber ship, that is said to be able to char an entire planet 3 times over. Well, that's planetary destruction. How can a Reaper actually stand up against that?.
And for that matter, the Mass Relays, if firing a weapon while in FTL will cause a planet destroying devestation wave. What happens when you disable the safeties, load up small ships with targeting VI's and such, and aim them at Reapers for an FTL suicide bombing?. I doubt they can withstand that kind of impact.
Especially when COMET struck a Reaper and "KILLED" IT.
But I digress, I see coventional victory as possible. Mass Effect has always been about achieving the impossible. The Reapers are fierce opponents yes, and they should be by all rights. The galaxy should be very damaged even if they are defeated. The problem however lies within the writing itself. I'm leaning towards Mac and Casey being the ones behind this. But there is definetly a conflict there where the Reapers are "unbeatable" because someone wrote it so, and where they are beatable because someone else wrote it so, and the very contents of Mass Effect support said outcome.