Tacullu64 hit the nail on the head. We really do need to find our balance or rate of Mage-specific, school-specific, and cards for anyone. I absolutely love this game and I plan to stick with it for a long time. So, I'm looking forward to how this game will evolve in the future. That being, there will be many more mages (hopefully) and a lot of them will share the same schools in some way, perhaps a couple that straight-up have the exact same schools, but function a different way. I really like how the Forcemaster gets exclusive access to a few spells, and therefore, a particular strategy. And, I also like how the Wizard can cross paths with the Warlord and Warlock in some ways. With this system, both you and your opponent know a little bit more about what to (or rather what not to) expect.
Another way to put this, I like to see it as the exclusive cards should serve as the basis for your mage, what gives them their identity and basic strategy. Without them, the only thing that really would set everyone apart in the future would be the special abilities on their cards and that some mages will have more of one element than another. Now I'm not saying we need even a lot of the cards to be exclusive, your mage's true power comes from all of the non-exclusive cards he/she has. I'm pretty optimistic about the future of Mage Wars, so I really think a few expansions from now, there will be so many cards and options that this whole deal with exclusivity will become sort of an afterthought. It'll still be there, but I'll just play with the preconstructed deck one time to get a feel for the mage and then my next deck will be entirely different if that makes sense.
Anyway, I thought the first expansion was awesome, way better than what I was expecting.