If anything the Lunar Gateway sounds to me a lot like "classic" Nasa risk aversion and over-preparedness. It isn't strictly necessary, probably, but it sounds like it makes lunar projects overall safer (in communications access at the very least, but also reusing ascent stages, and providing more backup habitat space in cases of disaster readiness) and that's still good science to prepare for risk. (They don't want a second Apollo 13, and who can blame them for that?)
> The only reason to even consider using the high moon orbit is to have something, anything for SLS to do.
It seems like that is already disproven. The first few missions to setup Lunar Gateway modules have already been scheduled on SpaceX Falcon Heavy launches (in 2024) so clearly even Nasa understands they may have to rely on SpaceX even for access to Lunar Gateway orbits because the SLS has already missed deadlines. The "traditional" flipside to political boondoggle politics is "standard" commercial bids and contracts, and Nasa is far too pragmatic to rest important pieces of a scientific mission waiting for the SLS as the "only option".
To disprove it, you would need to find something useful for SLS to do.
NASA, of course, has no say in whether to use SLS. Congress decides that. The best NASA can do is have it not ready to fly. The longer it takes to fly, the fewer flights they will end up forced to do.
The only reason to even consider using the high moon orbit is to have something, anything for SLS to do. Every conceivable mission scenario is better staged from low earth orbit, but they wouldn't need SLS for that.
And the whole point of SLS is so they can hand out $2B in plums to mil contractors for every mission, that they couldn't for a measly LEO launch.