That’s… extremely ignorant. TBC adds the BE/Dranei zones (which can get you to 20) and expands dustwallow marsh (helpful in the 30s).
The rest of the game is literally classic leveling, which anyone playing classic has just done.
Asking people who want to play TBC to mandatorily level a new character from scratch is asking them to play about 35ish levels of classic, and while it’s a bit faster than it is now it’s still a ridiculous wait to play the game you signed up for.
Some form of transfer is needed in order for the game to actually succeed. And in my opinion, it doesn’t make sense to make it arbitrarily meaner than it was in classic. No one stepping through the dark portal lost professions, that’s simply asinine.