That's really strange. I think the UX improvements were fantastic.
Given that KMail is really the only true open-source non-janky Android email client it's incredible to me that people can be so uncharitable.
With the UX changes came long-desired fixes. KMail may be the only O/S mail client at this point with a fully working IMAP search (after Apple Mail screwed it up years ago). Plus they fixed a super-irritating power mgmt issue.
I don't follow. The guy who presided over K-9 Mail's UX becoming terrible, will help improve the UX of Thunderbird?
No, your parent poster says that after Aqui-hire he might get pivoted away from it and hopefully the UX might improve.
I personally see this as a way for cketti to get acqui-hired and maybe get away from K-9 Mail. The amount of hate directed towards him from the userbase (mostly justified, sorry to say) has been substantial and I can't imagine he really wants to continue dealing with that.
Hopefully Thunderbird will do another UI redesign and fix the mess that was made. I ditched K-9 after the new design came out two years ago.