[ekingr]

I guess beyond UI/UX, a key pain point that webmail solved is synchronisation. Whatever the change you do on whatever device, the state is managed by the server and reflected the same everywhere. Much easier than POP/IMAP/Exchange. The drawback is that you have to be always connected.

[kwhitefoot]

Thunderbird synchronizes too. IMAP works online and I have a copy while I am offline. I don't see how a webmail client is any better.