I've used Evolution for years and couldn't be happier.

AFAIU it does not apply any heuristics but only checks if my email provider has marked messages as junk, plus what I manually mark as junk.

I almost never find a valid mail in the junk folder.

I suspect something went wrong in your initial setup, or you had some ambiguous/invalid IMAP settings in Gmail. And I'm going to guess that switching from Gmail's webmail to a proper email client can be daunting, because Google always likes to do things a little differently, often esp. to piss people like you off and keep them in their grip.

These are the only junk-related settings I have: