The thing to remember isn't about whether or not your the game is allowing your character is powerful enough. I'm certain your characters will be powerful as the game goes on. It's whether you're losing some fun value by not having less important skills available.
If my skill slots are very precious, it's hard to imagine keeping a skill like "Rain" equipped in the mid to late game for those times when it's minor benefit becomes very strong, when it's competing with a "Winterblast" and "Fireball".
It's fun to find combat solutions where "Rain" is the right choice, but if I'm min/maxing my character, I have to put a spell which is highly likely to effect the outcome of combat.
Additionally, there's even less incentive to sample a new skill tree for fun because you don't get any new skill slots for doing so.
That said, I still think Scrolls are probably the answer for this.
