The problem with that suggestion is that the old Gmail used to have the best UX out of all email clients—web or desktop. I preferred it over Outlook or Thunderbird. Now I'm begrudgingly using it unti something better comes along and hoping Google doesn't acqui-hire them out of existence.
I started using eM Client as a native desktop email app because of the new gMail reply feature. Feature-wise it does everything I expect/want for email.
It drives me absolutely insane when a company makes an 'enhancement' and reduces usable window space. If I am writing a long email I want to be able to use the maximum amount of window space and not be crammed into something that is 25% of my monitor size.