Do I need to refer to the math post again?
You can not account for combo-transformed skills, OGCDs, buffs, and everything else the higher level toolkit has without individually nerfing every higher level vs every lower level. You'd have a full ass needless database of "82 downsynced to level 47 dungeon", "90 downsynced to 33", "53 downsynced to 17". And by the way, how do you resolve a level 90 player and a level 76 player both joining a Level 50's DF? Which is to say, assuming same class, now you have to balance 90 vs 76, and then vs 50.
The only other way is a flat stat squish/reduction, but I mean ffs, you can SEE how poorly the rounding does with that. A level 90 person with Savage gear WILL outdps a level 20 person with the duty-appropriate gear, even if BOTH of them literally did nothing but hit 1 over and over (using the same cookie cutter base skill with the same potency). If THAT already fails to meaningfully "cap" the higher level player's damage output, do you really expect any solution applied to endgame gear AND skill rotations would work?
Literally everything would die in a single rotation by that point up through like SB or ShB. Wow, so much fun for the trial and/or new players, fuck em, right? So long as you can press 1-2-3-4-5-6-7 instead of having to only press 1-2-3, nobody else's enjoyment matters but yours.
This stuff's why every pvp game that balances off of pro player input has gone to shit. You think, and the devs think "oh, these people know what the game is like at the highest level, surely their thoughts will lead to the perfect game!", but it leads to 95% of the playerbase being completely turned off of it.
Max-level shit is only fun if you're max level. Everyone else deserves to have fun, too. You were level 16 doing Sastasha for the first time ever once, too. Edited edit: and see my post a few above, I'm aware the low level skill rotations are themselves boring. But part of the appeal is GETTING those skills as you level up. Before y'all start going "lol it's not fun to press 1-2-1-2 as a level 16 player", agreed, but they aren't level 16 forever.