Dropped $250 on a YubiKey bundle, now I'm questioning if hardware keys are overkill

Hold on, the backup codes aren't really the same thing as the YubiKey though... they're the thing that saves you when the key fails, but without the key, you wouldn't have those codes stored the same way. The authenticator app can do a lot, sure, but it lives on the same device that can get compromised or stolen, which is the whole point of the key being separate. SIM swaps are nasty, I've seen people get cleaned out, but that's more about your phone number being weak, not really about the app itself. If you're careful and your phone is locked down tight, then yeah, the $250 is probably overkill for most people. But calling backup codes the same as the key is kinda like saying a spare tire is the same as having four good ones, it only helps after something breaks.