I used Inbox for a long time, but in the last 6 months or so it has gotten so incredibly slow. I started going to gmail any time I wanted to go straight to an email or compose something.
Inbox was Google's chance to offer something compelling to help me handle email. Inbox was the prime candidate to be a Progressive Web App—it could have been offline-first, use Service Workers and Web Workers effectively to manage requests and stay super-responsive... it was promising. Instead it is what it is now, abhorrently slow and network intensive, with merely fringe "benefits" over the old gmail interface.
I'm going to be switching to Fastmail very, very soon. There's just no reason for me to continue using Google for almost anything.