I've been using Protonmail as my primary address for a few years now. I'm yet to have a single spam email make it to my inbox. In comparison, I use my gmail less and I've had a few blatant crypto scams make it to my inbox.
I'm not saying for certain that it's better than Gmail's, but that's my experience so far.
I've been using proton for a few months now with a yearly Mail Plus subscription and I have yet to receive an actual spam e-mail. Your experience might be different than mine since I take precautions not to invite spam in the first place, but even then, Proton looks to be doing an excellent job