This would be the case if many people get the quantum “crack” at the same time. Since it would enable a pre-image attack, one actor could selectively mine blocks for a considerable time until others catch up. This could be going on now.

Yeah, sway better strategy than dowing the world bitcoin is bust while holding it short would be to just mine blocks here and there, to steal from inactive wallets, etc.

I'd drain as much wealth from the network without being detected instead of going guns blazing.

Probably not since quantum computers don't exist.