When I realized I can't go back to normal UI, I immediatly downloaded Thunderbird and went back to e-mail clients. I won't bother with the new gmail. Fonts look horrible, it is slower and in the end there is less information density.
The new font weights have such a stark contrast, it's hard to look at. It's enough that I'm finally starting to piece together the parts to leave gsuite for my personal domains.
Did they take away the ability to use the old UI? I still have a menu item under settings that says "Go back to classic Gmail"
That menu item will vanish soon. Several users have reported it elsewhere in this thread (it has vanished for me too).