When Do Limited Options Become Stifling?

[Tanarii]

If my issue is about not being able to play a concept I like, then I am as likely to reject a game on the basis of the system as any other restrictions.

Agreed. And sometimes the worst GM restrictions are ones that attempt to make a whole system work like something it doesn't in pursuit of a cluster of concepts.

Take WotC D&D and anything inherently low magic. This includes basically any classical concept, but in particular it kills Swashbuckling Pirates / Musketeers and Medieval Knights and Vikings, but also Victorian unless you want to go full Magitech/Eberron-style Victorian.

And both TSR and WotC D&D can't handle Intrigue, Mystery, or Horror. Including things that are a blend like Werewolf/Dracula (c.f. see the failed attempt that is Ravenloft) nor Cthulhu.