Good points about the complexity, but perhaps it is to expect too much that dealers and sales people should even have a clue about this! I think your point about electricians saving some money is the real issue.
If you install a 50 amp breaker, my simple view is that you should have the cable...
I do not think it makes any difference at all when charging with AC up to 11 kW. There have been many Tesla’s that have charged daily with 11 kW.
secondly, if you really want to do this, you can simply dial down the ampers on the PMCC! I am not sure how low you can go but cerainly down to say 6...