I get that your buddy is in a bit of a tight spot, having removed that much muscle.
But the fact that you would rather go on the offensive about how GUE (and similar agencies) and their config is wrong and not a good fit for your mate rather than come to the very simple conclusion that you could just help your buddy get into his harness (I guess he didn't lose 90% of his movement range in the arm?).
I can get into my harness on my own and so can the people I dive with, but it is easier if you help each other (which is really what GUE is about, you're a team and you all help each other).
While it seems like you have already made up your mind about GUE, I still feel like you haven't given it a single look beyond the fact that your buddy can't use a certain type of harness.
Their Fundies is an extremely good class (and a great preparation for tech), doesn't matter what your goal with diving it, everyone can benefit from it.
My classmate for Fundies rented a BPW (single tank) setup that was equipped with Halcyons cinch system (which someone like your buddy would find very helpful).
You could at least try and talk to an instructor about the possibilities of that for a Fundies (which IMO is the best intro to tech class on the market).
Don't write them off the board just yet, there is no obligation to drink the kool aid and get a diehard subscription to the DIR system just because you take a Fundies.
Another question, that doesn't have anything to do with what organisation you prefer...
If your buddy has had that much muscle removed, and has that much trouble getting into a DIR harness, does he still have the mobility and strength needed in his arm to execute a valve drill with back mounted doubles?
Because I'm having a hard time thinking of any tech instructor who would pass a student in a tech class if they couldn't pull that skill off.
My buddy is, quite frankly, hardly a blip on the screen of why I won't work with GUE. Their curriculum is setup absolutely terribly (imo, as a person that designs training curriculum for clients professionally and have been teaching or developing training in some professional capacity off and on for more than 20 years). Their rigidity is theirs to have, but not something I'm interested in dealing with. Their belief that "our way is right and anyone else is wrong" is well known and while some may argue that no such thing exists, the agency literally still prohibits smokers because, well who knows or cares why but it's certainly not because they've done a professional medical evaluation to determine that no smoker on the planet is medically fit to dive, nah, it's just "their policy". They're welcome to have policies like that, but it's surely indicative of what kind of an agency it is. I don't smoke (haven't in years) so that requirement doesn't stop me, but the attitude it represents (along with sooo many other things about the agency) tell me it's not an agency that I want to have anything to do with, much less support with my money.
p.s. when you say "fundies is an extremely good class" the only possible way I can interpret that without laughing is that you mean "fundies lets people become better divers", because no "extremely good class" has as many possible outcomes as that class if it's designed even marginally well. If I tried to design a class anything similar to the cluster that is GUE's fundamentals course I'd not only be laughed at by my clients, I'd be fired the same day.
So no, it isn't my buddies disability that keeps me away from GUE, that's merely one example of one thing regarding the agency and their published standards and information among a much larger and more relevant list of things I fundamentally don't like about GUE.
TLDR: no, I don't like GUE and no it isn't because I've not looked into them at all, and I'm still not seeing any reason to reconsider my stance on the organization itself.