So in this scenario though, depending on the class, then both specs for the priest are “healing” and sure one may be optimal for AoE vs ST. Or efficiency vs throughput. But then they wouldn’t be able to swap to a DPS spec when you don’t need more healers, or have the ability to easily switch to a PVE farming spec. You lose the ability for warriors to go between tank and DPS as needed (or paladins, or druids to a lesser extent). So there are still trade offs with the system. There are still places you wont be optimal for the raid. And there are still places for a hybrid to exist.
In the example of the priest going Single Target vs AoE healing. In Classic now, the argument is you may spec hybrid so you can smite spam in dungeons / raids when you don’t need to heal, you can solo quests / farm easier, etc. If classic had Dual Spec today, though you say that the hybrid spec for that priest would be they would have to be AoE vs ST, OR Healer vs DPS. In both of those scenarios, there is a tradeoff where they are not optimal at something. If they go Healer / DPS specced then they wouldn’t be optimal for AoE or ST if they were a hybrid healer spec (the standard ones). Or they could pick up some of the AoE talents at the expense of others. But they could quest / farm easier. But on the flip if they talented AoE vs ST (or Regen vs Throughput) then they wont have those smite talents to do the farming.
If they went hybrid smite / ST and smite / AoE for their 2 healing specs they wont be optimal at either but still be a hybrid. There are ways to play into the system. The talent system in general offers a variety of talent choices, the meta is what dictates how the players play and what they do or do not choose to play with (look at all the threads about how rogues wont be invited to anything for all of TBC… Not that they can’t be good, just that they don’t fit the meta anymore).
Plus, we aren’t even discussing the super hardcore guilds because they will swap players / classes between boss fights to get the edge. This happened back then and it happens all the way through retail. It’ll happen in Classic TBC too. So for them Dual Spec wont matter since they’ll have people who have raid ready alts (of even the same class if they have to).
Not to mention in any of these scenarios where people are picking between 2 PVE specs, then there is a gimp to their PVP abilities too. So even if you let people swap in front of the bosses with Dual Spec, there will still be hybrid specs or specs doing off roles.
I know that classes are designed differently in WOTLK vs TBC and the paradigm shifted to bring the player, not the class. But even then when Dual Spec was introduced, there wasn’t rampant one-size-fits-all to the raiding scene. There are plenty of hybrid specs in the game. Even on retail where specs are locked more you will find people using certain builds that aren’t meta or optimal. They just wont be at the top of the DPS leaderboards basically.
I know my guild is not alone in this but we don’t know, and wont in TBC be forcing people to spec a specific way to fill the role they have chosen. We run with a boomkin now in classic because that’s what he wants to play.