Yes in theory, this will happen. We don't know what this will look like in practice. Not sure how an Arms Warrior with basicly no self healing or utility is supposed to do the same solo dungeon in Torghast for example, that a bear tank, or any tank, or DH or DK or Beastmaster will do. Either they have to balance it, that it is doable for speccs like Arms, which would make it ridiculously easy for a lot of the strong solo speccs, or they have to balance this kind of content to each specific class/specc, which would be a nightmare when it comes to the amount of work and ressouces this will eat up. So i'm really not sure what we will get here from the developers. It could become a major shit show.
The only somewhat simple solution in my mind would be class design like it was in MoP. Where literally each class and specc had self healing, utility and such, which would make creating this 1 to 5 instanced content much easier. But i doubt the class developers are able to recreate such class design if Holinka says that he is proud about what they have done and accomplished. Because bringing back some old abilities they didn't even create themselves and took away, because they have no clue, without proper class design and good synergy between abilities and proper mastery will be meaningless when it comes to fun class gameplay. So i very much doubt we will get MoP like class design, because this would certainly be a big class overhaul equal to Legion. But they clearly stated that this won't be the case.
Instead we will get a bunch of talent trees and abilities we will lose in the next expansion, again. On top of that, our characters will be different strength wise when it comes to open world, certain dungeons or raids, because we get extra abilities in Torghast or some abilities aren't active in PvP or Raids or only active in specific regions like it is in Nazjatar with Benthic gear. Which is garbage design in my opinion. Even in WoW Classic there was gear that gave me plus 1% crit everywhere in WoW. But apparently in BfA this bonus has to be restricted to certain content.