Supernova has fixed a number of the performance issues with large mailboxes, but that was fairly recent. People steeped in Windows still prefer the sleek/modern UI in Outlook over TB, in my experience, but the biggest benefit in Outlook is just the tight integration in MS/365 land.

Calendaring in TB always felt like a bit of an afterthought compared to email, and for personal use, that makes sense. For business, strong calendaring with meetings/shared calendars/availability and the tight link to meetings (Teams)is not done as well anywhere else.