Quote Originally Posted by NichG View Post
Well, its also communicating those things to the players sufficiently well that they actually feel it's legitimate to try...

'Hey guys, if you had wanted to jump the castle wall, you could have just done it' doesn't do much if no one at the table understands that (and when) it's going to be e.g. 'trivial and within genre conventions - don't even roll'.

When you get to really high end stuff, and I don't just mean something that can be done with a 3rd level arcane spell, consistent conceptualization is the hard part. Like 'Should I even think that shattering time is a thing I could do with my insane strength? Is that on the table or not, and what does it even mean if I did it?'. This is more an issue with high end shonen stuff (or superhero stuff) than high fantasy per se, but its definitely a thing when you start to get really crazy power levels and you don't have a consistent rubric to say what those power levels actually mean.
Does high fantasy begin when someone can shatter time with their muscle strength? Because again, Lord of the Rings is high fantasy. If that is the lower bound then level 1 D&D 5E is already high fantasy if the DM makes the scales of the adventure epic. It's not what the PCs can do, it's what the game is about. The "high" in fantasy is something the DM decides, not the players and not the books.

If the lower bound of high fantasy is Goku exploding a planet with a ki-ball then D&D becomes high fantasy when the DM allows a 17th level wizard to use Wish consequence free.

Considering these goal posts are so far apart that you can't even see both of them the only way to answer this question is for the OP to define what they mean by high fantasy, since they're not using the conventional definition.