Yea, I think/hope they’ll emphasize that rule in the revision, rather than it’s current status of being under the radar RAW.
Yeah, in its current state, even though it is very clearly allowed by RAW, not even called out as optional, it
feels like cheating. Here’s this list of backgrounds that each give specific proficiencies, equipment, and abilities. Sure, it
says you can change a background if you want to, but it doesn’t seem like you’re really
supposed to. Like, maybe ask your DM if you can swap out a proficiency if you already got it from your class, but don’t mess with it
too much. Otherwise, why would they be presented in complete packages like they are? If you were supposed to just be able to pick whatever two skills, two tools/languages, trait, and starting equipment you wanted, they’d just say that (nevermind the fact that custom backgrounds are also a totally RAW option).
If I had my druthers, custom backgrounds would be presented as the default option, with the pre-built backgrounds as
examples.