Protonmail is perfectly safe (for now) as long as you use it through Tor (https://protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7...) or a VPN so they don't log your IP and don't provide real recovery information.
And if you're restricting your conversation to people on protonmail for security, why bother with email at all? Seems easier to just put the conversation on signal anyway. And then you get all of signal's other security benefits, like E2E encryption, crypto ratcheting, disappearing messages and so on.
This second restriction is especially damning: They accept cryptocurrency, but only for existing accounts - after you've already doxxed yourself.