I do not agree with this completely.
The right tool for the job can be sidemount for beginner divers when they cannot carry their cylinders on the back. Sometimes the strict rule of the tool is too rigid. For example I had a diver in a wheelchair who wanted to do cave diving. Not that serious stuff, but at least cavern and a little bit into complete darkness. The diver was able to fin on itself, but only with splitfins. The diver was able to dive with a drysuit, but had a big pushbutton from doors in a hospital and so to fill the drysuit with air. In a real problem, the diver was able to close the valve on the back, but the diver was not able to use a normal inflator, so had a bcd with a handle, an Aqualung Ixiom. This bcd is not suitable for a twinset. But you can attach a ponybottle or stage cylinder and then you have made a twinset.
We have teached the cavern course with 2 instructors and went on the last dive 150m in a cave. The dream of this diver was fullfilled. All was done according to standards (the cavern can be done with single tank, but was not allowed in the cave we teached it as we needed a permit that stated 2 cylinders, with on both cylinder an spg, even if it was a twinset), but such a thing is impossible with gue. Not all divers want to do exploration and some are not able to. This diver wanted to know what cave diving was and in the 6 dives we did, the diver explored on his own level. Now the diver wants to go to Mexico for some guided cavern diving.
Another diver I know has his ankles fixed rigid in a 90 degree, otherwise walking was not possible anymore. He has done a fundamentals course, but failed. And only because of his finkicks are not as they have to be. But he can't use his foot like we do. He now has a ccr, dives without problems on wrecks to 100m.
These examples still have the team spirit, are teamdivers, AND can have in my opion the gue mindset, but cannot use the tool that most people can use. But they are not unsafe, they found a way to dive and to dive safe.
So use the right tool for the job, yes.
But in my opinion you must be more open to other configurations.
Why is it unsafe to do a cave course in sidemount config? What is the problem with that?
What is unsafe with sidemount in open water?
I agree that maybe sometimes too much courses are made to please divers, or to sell cards. But there is a market for it.
Also, what changes my teamspirit mindset/gue mindset when I use sidemount in open water? Nothing. Also if someone uses a normal bcd.
But use the right tool nowadays like ccr and sidemount was a wrong tool in 2010. So also gue changes. And I guess they will change in the future too like others do. The Shearwater computer is now also accepted.
In 2010, there was also no dpv course. Now they have.
DPV in open water courses, also from gue, are most times sold as 'fun', so is that tool needed then? Most times absolutely not. But yes, diving with a dpv gives a lot of fun.
CCR was first only possible after T2, not already after T1. This means they also change here. Why was it in earlier days not a right tool before T2?
So the right tool is in my opinion not part of a gue or dir mindset. You must look at safety. Is the tool safe? What is the problem when using it? Nothing? So why is that then wrong?
But I agree that starting open water diving with a ccr is the other side, I have never teached that. But I have seen some advanced open water divers with a ccr that can use this tool really well. But photographers are most times not diving according to 'gue mindset' as they are really good solodivers