I agree completely.

It is obvious that SE re-balanced everything to point to level 70, which causes everything to essentially be build-up, which is nice, but I think the systems need to be better articulated. What the OP suggests is one branch, getting the class mechanics early and being able to tweak them with talents (which, admittedly, is crazy difficult to even think about balancing) I think another option is to make the classes more dynamic and add mechanics at different levels, for instance, for most all classes the gauge is introduced at 50 or 60, perhaps add it in earlier and just change the sorts of things you can do with it, such things becoming more epic as you reach 70 wherein you unlock your uber skill or whatnot.

I think the effect of such a change would be to make leveling unique and fun even at low levels, because right now all you can see is the skeleton of whatever you're going to be at 70 and that's really depressing.