Threading: You're right. But I tend to find the UX around grouping to be confusing and hate the cruft of signatures. Besides, why do seemingly all E-Mail clients want to show the text at full width? That turns the majority of E-Mails into one very wide line. Not only does that look dumb, it's also very far from the optimal reading width.
It may be "outdated" or whatever, but adoption wise E-Mail is an amazing protocol. But show me a client that doesn't suck (my current favorite is mailbox.org (io/ox) with some customizations (https://gist.github.com/solarkraft/6afcfff8d5283cefad40695c9...) but that too is far from perfect).
mutt ("All mail clients suck. This one just sucks less.")
Yes, it's text. It's also extremely customizable, the polar opposite of the current fashion of locked-down proprietary clients where nothing at all is customizable. Mutt is amazing.
It may be "outdated" or whatever, but adoption wise E-Mail is an amazing protocol. But show me a client that doesn't suck (my current favorite is mailbox.org (io/ox) with some customizations (https://gist.github.com/solarkraft/6afcfff8d5283cefad40695c9...) but that too is far from perfect).