Undrave
Legend
Well you are wrong, I absolutely love fun and humor, in context. And that is the problem context or call it fluff, many of the new subclasses bring fluff with them. Take the PDK for example, it requires you to have a knightly order of purple dragon knights. There is one in Cormyr, so no problems for FR.
There ain't none in Ansalon or Athas or Oerth. Some of these campaign worlds have different knightly orders so creating a subclass for that would be in order in my pov. Some have none so any discussion about it is pointless. Athas e.g. in my book and many of the people who are much more invested in that setting does not even have paladins.
But none of the class features rely on there being a particular order. Your Purple Dragon Knight could just be a regular Knight with some specialized tricks. It's why they mention that outside Forgotten Realms they are called 'Bannerets'.
I think that aside from the Warlock none of the classes are so wedded to their fluff that they can't be hand waved into any setting easily enough.
This way you might be a little bit less flexible but you can have a lot of combinations and some specialized subclasses like arcane trickster are not needed.
But some of those 'Just do it with MC!' subclasses, like Arcane Trickster, Eldritch Knight or something, have unique features that you can't reproduce otherwise, like the Mage Hand Legerdemain.