It may be, if we only have a total of 8 active abilities spread out over the base class and whichever spec we choose. However, if there's more than that, say half again as many or more, it's going to turn into a game of metagaming the encounters, and adjusting skills and tactics for them. I don't know how much this could happen, none of us do, the only real example we have of the trees is an alpha build for a demo that may or may not make it into the game, but if we're talking 16 to 20 active abilities, there will be no such thing as an "ideal" character build.
Building off what I said in the Tactics thread, the game really looks like it's giving the player enough ability points to max out 2 base trees and a specialization, though you are free to invest in other trees if you so choose. If the level cap is 30 and not 25, that means we'll likely acquire 29 ability points, since the system almost definitely appears to be a 1:1 ratio of abilities per level. The base tree we've seen have all been 9 or 10 skill with 3+ upgrades each. Both Specializations we've seen have been 7 abilities plus 3 upgrades. So that's around 30 +/-2 or so abilities total on average for two base trees and a specialization.
Say you're a mage focusing on Spirit, Winter and Knight Enchanter. At level 19 you'll be able to have all the abilities in both base trees, 10 total active and 8 passives, by level 26 you'll be able to have all 7 abilities in the KE tree, 3 active, 4 passive. After that you'll have 4 more levels to then choose between the remaining 8 upgrades spread across all 3 trees. That leaves your character with a total of 13 active abilities, and 12 passive abilities at level 30. So that's 5 abilities more than you can use at a time. Not a huge issue since again this is a level 30 endgame character. We don't know how much we'll need to alter our loadout, they've said not often at all, but going by the ability spread having a high number of abilities is an endgame problem, where we'll be quite familiar with our characters and enemies so it's not like it will take a whole lot of guessing as to what abilities to roll with as well as if and when you may need o retool your loadout.
Even if say you got all the abilities in your Spec, 7, and then used the remaining 22 ability points spread across all 4 base trees you'd still end up with close to the same spread depend. 12 passive abilities, and then 17 active abilities if you just go for actives or 14 passive and 15 active if you focus on just two trees after getting the first 2 active and passive abilities for each tree.
I'm not sure you could really get that many more active abilities, unless you were specifically trying to acquire them, which you wouldn't because the game only allows you use 8 at a time, and you would be wastefully acquiring abilities you can't use to become a jack of all trades character that runs totally against the party based system. So it's kind of a moot point.