This is an interesting idea and got me thinking about it. I think the way you have it proposed would be imbalanced and probably wouldn't work out long term (as stated). Here was a couple ideas on other ways to do this. This is just theroycrafting and would need some play testing to get the proper balance (all numbers are being used as examples and would need to be tested to be confirmed).
Each players starts with normal stats and 120 point spellbooks. But, spellbooks are limited to 30 cards total. Players must stick with the same mage throughout their "career".
After the first game:
Winner = Gains access to one new school of magic. Or if they select the school that is their opposite, it goes from costing x3 to x2. (Example, if the Warlock selected Light, light spells would now cost twice as much, instead of three time. If he selected War spells, they now cost face value, instead of twice as much). Additionally they can have +3 more cards in their book (total 33 cards, still 120 point limit).
Loser = 2 additional cards in their book (total 32 cards, still 120 point limit) and gains +1 channeling.
This gives the winner more flexibility with their spell books. Spells cost less, but they are limited to the number of spells. The loser doesn't get that flexibility, but has the possibility to expand their books (to help counter the winner spell book. I see this as a type of side boarding) and they get a slight advantage of being able channel more to counter the winners flexibility.
So the way I see it, if a winner keeps winning, their spell book becomes more flexible, allowing them to adapt their strategies and change them in unpredictable ways. While the losers book becomes more specific, trying come up with the winning tact and being able to execute that strategy more quickly (due to higher channeling).
I could see some sort of tier system, if someone wins/loses enough matches they gain additional benefits. Perhaps increasing the spell book points, starting mana, life, etc. Could also grant starting equipment, critters, or conjurations. But it all needs to have some semblance of "balance" to it. You can't give the winner more things to let them win more quickly. It needs to be balanced, and if anything giving the loser more ways to win. This system rewards flexibility to the winner, giving them options to try out weird strange combos that usually wouldn't be available to them, while the loser gains more power to execute their spell book more efficiently.
