> This is very subjective; I hate it ;). I consider Apple's Mail.app/Calendar.app/etc much better UI-wise.
Agree it is completely subjective - and I actually think that the Apple apps look better and are simpler to use, but personally I spend a lot of time in emails and arranging meetings, and I can get what I need to get done faster in Outlook (although I have tried to get along with Mail/Calendar in OSX, it's just slower for me).
For instance, let's say someone writes an email to me with 10 people on copy and says that we need to organise a teams/zoom call (which is a pretty common thing), the workflow for this in Outlook would be 5 clicks and can be done entirely within the application (including creating the Teams/Zoom call link). In Mail.app/Calendar.app it's way more involved and you get lots less control.
But if you just want a casual email client, then Mail.app probably does what lots of people need it to do. So when I talk about good-UI for me personally, I'm not necessarily talking about it being beautiful, but I think Outlook is more functional specifically for a power-user.