Concentrating resources on one build type is completely reasonable.
But I think it will be hard to persuade current community users to switch to official if the situation will be as you described that official builds of new Android versions will only get released after an OTA upgrade to the new Android version was made possible, which might cause a huge delay because of the extra development and testing effort involved per device and per upgrade step, as is evident currently.
And I don’t think the resources which dropping community will free up are going to improve this situation dramatically (as community is easier to handle as you described), or does your internal math suggest that this will work out to everybody’s satisfaction?
Currently I’m expecting just a cut instead of persuasion, and this is totally not a problem in the moment official caught up with the Android version, but it could become a problem later with new Android versions and the OTA upgradability requirement.
I’m not advocating for keeping community in parallel to official on a device, and I’ll just deal with any situation at hand when it comes around without much blinking of an eye. This is all banal problems here, other kids are starving as the saying goes (or get bombed or shot).
But persuasion would look like this: Once official caught up to the same Android version community is on, with community builds then being stopped, Murena would just get the official builds released onto the download pages for manual install continuously including new Android versions as was usual not so long ago, then do the occasional OTA upgrade for users who want to wait for them without blocking manual install in the meantime.
Minimal friction and potential dissatisfaction.