They're also based in [edit: I thought Protonmail was Russian based, but they're not]. I think that's probably worse from a country level.
Encrypted email is a bad way to do private communication - services that pretend otherwise set off alarms for me.
The main advantage of Fastmail vs. Google is that it's a separate service focused on providing you a good experience with custom domain support. The business model is not ad driven so incentives are more aligned and it lets you leave Google services.
The privacy people's faith in proton is misplaced (imo).
No, they’re based in Australia. They’ve been blocked in Russia recently though.
If your concern is with state-level actors with the ability to do mass spying on emails in transit and collection from many different providers, then no, Protonmail won't be that useful. If your concern is with someone getting access to your email archive, possibly years after the emails have been sent, then Protonmail does offer something: even if its own data storage is compromised, your emails should be secure. I suspect the latter is actually a much more common problem than the former, as we've seen with data ransoming lately.
Unfortunately, Protonmail's implementation is rather clunky. I actually would consider using a self-hosted system that did something similar: get clear-text emails, but immediately encrypt them with a key that the server doesn't have the private key for, and still allow searching and notifications in some way.
My personal approach is to treat email as public communication and to delete archives aggressively.
I recognize that this isn't something most people do.