First be very weary everybody as this may get closed because everybody wants to chime in with their possibly related issues. Yes, I totally understand you are all having similar issues but that is still no reason to post your own experience.
Now, for the update. Yes, they did mention in their changelog:
Removed Options Panel and Moved Settings to Customizer
Emphasis on the moved to customizer. Because it is a theme hosted on www.remarpro.com it does have to abide by the requirements set by the theme review team.
So with that out of the way, let me chime in on this:
My biggest concern is that My Theme Shop has that much power over the functionality of my website via updates (especially since I did not prompt the new update to install).
@bhookedcrochet
I’m not quite sure I follow. Themes have no control over site functionality and shouldn’t. That is a requirement because themes are meant to display user content and not add functionality as it will get lost upon theme switch. If anything that sounds like either a site setting or hosting setting. Themes are not allowed to touch update system. I would highly recommend reaching out to your hosting company about that.
For the OP ( @kouya ), what I’m wondering is if your original question has been answered sufficiently or if you would like more information regarding the update? From trying to read all the comments it appears you may be having some issues with styling? If that is the case can I ask you please open a new thread about that so as not to flood this one?