Earlier quoted context omitted.
Me to, personally I drop GMail for a personal mail (20 euros per years, with a bunch of mailbox + unlimited aliases altogether with a personal domain. Benefit: alias to tell anyone a different mail so I know where the spam came from and I can easy drop anyone I dislike. Lightweight webmail (Roundcube) instead of monsters like actual GMail, login with user and password visible at the same time without the absurdity of…
Roundcube is everything but not a replacement for Gmail. I have my Gmail account logged in on 3 PC's going back to IMAP and Thunderbird never.
I also agree about TB, classic MUA seems to be remained in the 90's however at leas for us not-basic-users notmuch-emacs, mutt&forks, pine&forks, mu4e etc are valuable options, long to setup-up, mostly because anyone have a personal recipe and no one offer a ready-to-use solution, but far more powerful than any webmails.
However mailpie can be consider a good GMail-inspired webmails and IMVHO for most of mail users Roundcube even if is really basic it's enough, clear, simple and effective. Contacs are a bit limited compared to Google's one but the rest work well.