The Angry One wrote...
Easy. BioWare retconned Sovereign into only destroying 8 Alliance cruisers.
That makes a Reaper a glorified dreadnought.
Dreadnoughts and cruisers with thanix cannos > Reapers.
I don't think this was a retcon. We only saw Sovereign blow up three or four Alliance ships, and a few more were lost saving the Destiny Ascension. Furthermore, we don't know if the 8 ships mentioned are the ones lost saving the Destiny Ascension, or throughout the entire battle (remember, whether we save the Ascension or not, Sovereign seems to destroy the same number of ships in the same cutscene). The Alliance's light losses are simply because they came in after much of the fighting was done, and hit the geth from behind. Sovereign itself didn't even really participate in the battle significantly - we never saw its full capabilities - didn't see it fire on the defending Citadel fleet, and by the time the Alliance fleet arrived, it was attached to the Citadel, so fighting at a disadvantage. The Turians, however, lost something like 25 cruisers in that battle even if we do save the Ascension.
As to how we will defeat the reapers, it seems unlikely we'll face them in some sort of ship-to-ship combat. After all, this is an RPG, not a flight sim. Our success or failure will ultimately rest on Shepard and two teammates fighting some sort of 'boss,' on foot. Any speculation on reaper vs. fleet tactics is only really significant as far as 'what will the fleet do to delay the reapers while Shepard obtains and uses the MacGuffin?'
As far as destroying reapers in space combat goes, the derelict reaper shows they are vulnerable to kinetic impact, just like anything else. You hit something hard enough, and it will be destroyed, whether that's a ship, a reaper, or a planet, for that matter. What's the easiest way to produce a weapon out of existing technology in Mass Effect? Something that people often forget is that it is essentially impossible to create faster than light travel without also creating a weapon of unimaginable destructive power. Simply stated, if we really wanted to use logic to suggest a method of destroying the reaper fleet, we would construct a class of ships that have very powerful mass effect drives so they can maximize their FTL speed. Then just crash into the reapers while traveling at FTL velocities. Even a small ship traveling several times faster than light would impact with truly absurd amounts of energy.