I adore Garrus. I had him with me all the time in ME3 and reasonably often in ME2. Mostly for the lolz of his commentary, to be honest. I teared up when Shep was saying goodbye to him on Earth. True story. Though Thane was still my main guy There's more than one way to skin a cat. Just because ramming an asteroid into a relay creates an unstable detonation that destroys a system doesn't mean that every possible method of destruction would do so. Clearly from what we see the crucible, using a Reaper catalyst and being used to destroy Reaper tech, is able to sort of short them out and contain them to smaller explosions.