Lots of good advice & observations in that vid. Some things he mentioned, I’ve found echoes of in other creative endeavors- music, writing, art/design.
I’ll note one thing I’ve been doing since the early 1990s that dovetails off of his first point: I maintain a file of certain character ideas I’ve modeled in multiple RPG systems.* Most of them are statted out & built conservatively, using commonplace starting experience points (for that game) without relying on creative rules interpretations. This obviously allows me to join games in a variety of systems very quickly.
But it ALSO serves to train myself in how to adapt a concept to a setting. One- Slapstick, the Killer Clown- was essentially a mercenary who had a clown/jester visual aesthetic & a dark sense of humor. Kind of a more heroic version of The Joker or The Comedian. I made versions of him for 2Ed D&D, GURPS, HERO, TORG, RIFTS and a few others.
Because the RPGs themselves can vary so wildly, the characters can seem very different in their “final form”. Looking deeper, though, you can usually detect the commonalities between the versions.
If this sounds at all familiar, you may be familiar with some of Michael Moorcock’s fiction. IOW, I handle each of these PC ideas like a version of his Eternal Champion/Eternal Companion characters.
* most of them are initially modeled in some edition of HERO or in D&D 3.5Ed