User blog comment:Ironreaper/Retcons and Contradictions in the Reapers/@comment-2250460-20120415175600/@comment-4950455-20120416010028

And the Codex entries on The Reaper War establish that the turians, at least, have been able to take out several Reaper capital ships (which I interpret as Sovereign-class). I don't think there's any real indication that they're supposed to be as indestructible as you're saying.

Did ME3 retcon individual Reapers to be more powerful? Possibly, but not all that much.