I have exactly the opposite experience. Using outlook for mail is such a pain to me. Particularly the search experience does not work (I use expressionsearchNG for thunderbird) . For calendars it is just the opposite so that I am currently running it side by side. One problem is I think the iCal bridge to the outlook server we have to use at work. The announcement unfortunately cannot change anything here. I used the EWS addon maintained by Ericson [1] for a while. But Mozilla I guess drove many Plugin developers away by breaking the interface rapidly. Now they are putting some stuff into the core again. I am not really sure if that is a good strategy. They should rather IMHO work on a stable interface.

[1] https://github.com/Ericsson/exchangecalendar