I remember finding Mailtrain in my search, but the last time I looked, I don't remember seeing some of the details that I'm now reading on their Github. Apparently they can read bounces from more than just the services you named (which itself is a good improvement over Amazon-only), but can read from ZoneMTA and Postfix logs as well which is awesome and solves my "someone else's basket" concerns.

Thanks for prompting me to take a look at them again!