It's too bad their app doesn't have offline support. I use that feature of Gmail app a lot
On iOS and macOS I just use the standard Mail.app. Works well and even push notifications work.
IME, that's my biggest complaint. Even plain text emails take 2+ seconds to load.
Somethings wrong or suboptimal for you. Just tested this in the middle of the US with some messages from years ago to make sure they weren't cached and it was like 2-3 tenths of a second.
I actually enjoy watching it tender at light speed!