it does sound like you've had a good bit of experience and testing with Plesk so that may make you more comfortable with it.
cPanel does support MariaDB now as an alternative to straight MySQL but not Percona as of yet. Our XF install is also sitting atop MariaDB but we run headless custom systems for most items since they are task specific.
Nginx is also an option but only in a reverse proxy sense with cPanel, the only full Apache replacement for cPanel right now is LSWS, which works quite well but does add licensing expenses there.
You are correct that Plesk is lighter weight than cPanel since cPanel tries to pack so much into the user experience and gui it does add a few pounds if you will.
I've never personally tried out Rainloop, would just be a matter of how well you can get it to integrate with the Plesk control panel. The downside of most panels , cPanel and Plesk is they tend to like to control fairly tightly the items they install, so if you modify them outside of their acceptable methods sometimes un-intended consequences do pop up.
At the end of the day it's going to be a personal preference thing. We do sell on magnitudes more cPanel than we do Plesk, a lot of that is in part to the random issues Plesk use to have with breaking its self, especially when upgrading between versions. 9x-10x and 10x to 11x generally caused quite a few headaches. I will say as well, that the back end tech support (that we receive) for cPanel is far superior than that we receive from Plesk. Assuming it's an issue we can't resolve (which is very rare) one takes about 1-4 hours for us to get reliable answers where as the latter I've seen take a week + with Plesk.
In the end however, go with what you are comfortable with, we support either solution and will keep you rocking along