As someone who has hated something like 85% of all recent app redesigns with their wasted screen space and needlessly floating elements, Thunderbird's is one of the few that I actually kinda like, after I took a few minutes to tweak it to my liking.
That said, I completely understand the impulse. I do this a lot nowadays.
Something to keep in mind is authentication methods if you're using Thunderbird for certain accounts. Like just this year Microsoft broke QAuth functionality with Thunderbird, and I'm pretty sure you can't set up QAuth2 on Thunderbird 78 (at least without an addon).
You can probably count on that sort of thing happening more and more.
That said, I completely understand the impulse. I do this a lot nowadays.
Something to keep in mind is authentication methods if you're using Thunderbird for certain accounts. Like just this year Microsoft broke QAuth functionality with Thunderbird, and I'm pretty sure you can't set up QAuth2 on Thunderbird 78 (at least without an addon).
You can probably count on that sort of thing happening more and more.