I don't ever use their webmail, to be honest. I've got native mail clients on my devices that I connect to Fastmail with IMAP. To compare apples to apples it seems most relevant to compare storage tiers, MXroute is 5/month for 20gb, Fastmail's 5/month plan is 25gb (but single-user only).

I personally don't really want to deal with cPanel, too. Not because cPanel isn't cool, but because I explicitly wanted to pay somebody to do the management for me so I didn't have to get too in-the-weeds. I'm certain I'd misconfigure something somewhere and I just don't want to deal with that.

EOD it seems mostly like personal preference and how much you want to tinker. Value for both seem close to the same.