I didn't find the chats/discussion UI at all clear initially, but once I'd had it explained to me, I could see what was going on.
(I do remember it taking a long time to load, and apparently using a surprising amount of memory once it was finally done, but aside from providing reliable fodder for water cooler conversations with other 40+ year old colleagues this never actually seemed to cause a problem in practice. At my last Teams-using job I would restart my PC no more than once or twice a week, something I could let happen in parallel with making the cup of tea that I'd always be making at some point anyway. And it had 64 GB RAM, which isn't even a lot by today's standards, but still Teams didn't actually fill all of it.)