Oldgit, not so much an issue with bike fitting, more what people choose to do with the information it provides them.
I'd hope that if I did go for a bike fit then I'd get an optimised fitting on specific bikes for a specific purpose (e.g. I'd expect the position on the TT bike to be distinct from the road racing bike.) I'd take that information and add it to the pot of existing knowledge and just not blindly apply the results. And I wouldn't expect that information to then be carved in stone with the passing of time and bikes.
I suppose it's like any other tool, power metres being another good example, you need to have a bit of understanding to interpret the data that they are providing you, otherwise it's a bit of a waste of time and money.