Is there a meaningful distinction to be made between the system and the content?

[dafrca]

D&D isn't generic. D&D is constrained in genre (and that genre is not "all fantasy"). It explicitly does D&D worlds, not "any fantasy world"--it's not an emulator, nor is it trying to be one. Maybe to make the difference, D&D should get moved up the scale to the 30s, with PF being removed from 40 as an example and being lumped in with D&D. Maybe (?) replace it with Starfinder, which is more setting tied. I think.

I agree 100% with this. I remember how hard me and one friend tried to port over so many things to D&D and failed to keep the feel we wanted. They all ended up feeling like Greyhawk or FR.

I also do not understand the treating PF and D&D as different levels when PF is D&D with a different colored dress on.

I know it is a very old niche game but Morrow Project's rule set was very tied to it's setting and it was very hard to split them apart. I wanted to use my Traveller rules to play in a Morrow Project game, it was super hard to do. The effort lasted a few months but died under its own weight.