I don't anticipate you'll be thrust into a situation where you have zero idea of what to expect combat wise unless you aren't paying attention.
(Sameul Jackson voice) Lady, this is an open world game where enemies tear out of other dimensions, spring out of swamps, hide in caves, and you're saying that you won't need to anticipate such situations? How do you anticipate a situation that is going to change by the second? How do you anticipate a group of enemies ripe for being Fireball-ed only to realize you don't have it on the quickbar?
Paying attention has nothing to do with it when you're in a game where combat takes place in very diverse environments with very diverse set of enemies, not to mention combat itself is ever changing. I'm not saying you can't play using only 8 abilities, only that it does nothing except frustrate the player by limiting him from taking actions by design.
Sorry, but this is a weak design where the player is constantly reminded of his inability to use his full array of skills to control the battlefield and is preoccupied with thoughts such as "I could've used that talent right there because the enemies are in that position now. I can't because the talents are locked down, maybe I should just reload.", as he's losing.
They can paint it anyway they want. Throw words around like tactics and strategy as much as they want. It's not going to change the fact that they tied up gamers' hands by implementing this limiting design, all done for the sake of "console parity" and multiplayer coherence. I'm not mad, I'm just disappointed.