Yes, I believe you are correct; those problems are locked into firmware as part of their FCC certification for Part 95E.
One solution, I believe, is the Baofeng UV-13Pro. It is the Ham Radio version of the GM-15 and is open to GMRS frequencies.
As such I believe all channels are programmable.
If that is something that you are interested in, I have one here (I purchased it from AliExpress for about $20 including free shipping) and I could run the software and see if I can populate GMRS Repeaters on the other channels, as well.
I do not recall if Chirp supports this radio, but it would not surprise me if it doesn't.