I've left Gmail for Tutanota a long time ago. I prefer having a niche service that focuses on privacy and is committed to open source. They'll even release the app on F-Droid soon, couldn't be more psyched: https://tutanota.com/blog/posts/secure-mail-open-source
I didn't compare much, but to me Tutanota is exactly the opposite to Gmail and that's what I love. It's ad-free, no tracking, no scanning of data. Once it has the app on F-Droid it's the only email service (to my knowledge) that enables you to use it without any attachment to Google.
Hey man, email existed before google :) You can use whichever email service you want that's not google and use an open source email client like K-9 Mail or AOSP's Email client :)
Only non-standard emails won't work with POP3 or IMAP protocols. In those cases you need to use their specific program/protocols, yes. It seems Tutanota falls in this category, as does ProtonMail.
