After figuring out that gmail login will only work with cookies being enabled in the setting I am super happy to finally have a sane folder & filtering interface. I'll probably stick with google's UI for the agendas for now, but overall this is being really smooth.
Ironically, the search in thunderbird, while not perfect, is so much better than on gmail, where I often have trouble finding emails from half an hour ago, searching for the exact subject line.
EDIT: and spam filtering! It's amazing how many really important emails gmail flagged as spam for me. Like, mails coming from colleagues on the same custom domain, as replies to emails I sent them. I really don't get why people use google's products, honestly. At this point it's just pure monopoly I guess, and increasingly network effects since the big providers don't play well with smaller ones.