I would say that removing world buffs, killing pre-nerf drums before that whole thing got going, the regen buff hotfix, and the feral energy change were all within the spirit of what TBC “should” be, where the change was meant with the express purpose of trying to make sure the experience is more like TBC, even though they’re making unprecedented changes to achieve it. For example the regen buff hotfix. Ferals were slated to have, without question, the absolute worst rotation in the history of the game, all expansions or classes considered, if that wasn’t changed, and nobody knew about it back then. It would be a completely different experience than original TBC. There’s also the fact that it just made no sense to leave it untouched, it was an absurd mechanic.
I would say that dual spec does not do something similar.
It’s simply a player convenience people want…because it’s convenient and lets people be lazier. It’s not a feature that aims to achieve any sort of TBC-vibe that could be lost due to modern player habits, it’s not a change that would be made to balance out the 2021 WoW players knowledge of the game. It’s not a change meant to fix what could be considered a crippling error in the original.
It’s simply a nice-to-have that presents a major, undeniable boon to players that they didn’t actually have back in those days, and I don’t believe anybody should have access to that boon because it creates variables for approaches to TBC content that simply wouldn’t exist otherwise, and never did exist. It would create certain metas or scenarios of optimization that are completely alien to the TBC environment/sandbox. It’s oddly shortsighted to think that this simply won’t affect anyone but the people who pay to unlock it. It affects the entire game and everyone who logs in. The efficiency and versatility of players drives so many external elements, it’s hard to think how that even became an arguing point.
Similarly, I thought the (one time) boost was horrendous too, and the fact it’s something that never existed is maybe only half the reason. The arguably more pressing reason is the opportunity it presented bots to abuse and we all know to this day that TBCC has a massive botting issue.