That's not really true. Talents which are large CDs can't be switched out of quickly right now because you have to wait for the CD to be up. All this means in reality is performing significantly lower in terms of throughput or not having a CC ability that's suited to the thing you're about to do.
The concept of making an AoE mage and being shit at ST and being stuck that way is 1990s thinking. It's also undermined by the fact that you can switch specs already, so I could make a fire mage specialized in AoE and an arcane specialized in ST and then just spec swap. So this doesn't actually even implement such a limitation.
It's just a massive annoyance that effectively provides nothing to the game except making the option of uninstalling more appealing.
TFW the devs don't realize that this negatively impacts those of us who carry LFG and LFR content. "group" content where not a single person other than me is going to put up the cost of letting me and anyone else talent switch in order to maximize the group's performance.