As a 20 years Gmail user, in case anyone was interested ..
I did a long evaluation of Proton Mail vs FastMail vs Infomaniak Mail trying to see which one is best.
FastMail won out, as it was the most compatible with my Gmail programed brain. It's features lined up most closely…
I migrated one of my email addresses to Proton a year ago, and I'm absolutely happy. I'm not experiencing any slow page loads, honestly. It's super fast for me.