Humans may dwell here

Alex, after consulting with a group of experts at two conferences, we came to the conclusion that magic is completely unusable. With the number of available skill points and the exorbitant requirements for spells, it's practically impossible to create a viable magic user, and in any case, you'll have to resort to cheesing and min-maxing. Mana costs of 300 with an 85% chance of failure are simply ridiculous. When you need to spend half of all your skill points just to build up a mana pool to have even a minimal chance of casting this spell once (with a 50% chance of failure), and spend the other half on buying this spell and a couple of other equally useless ones – that's not cool. In your system, a mage is doomed to rely on a couple of weak spells, investing the rest in a hybrid build, or trying to cast one powerful spell twice before some backwoods yokel comes along, picks his nose, and whacks him on the head with a club.
Personally, I didn't look at how fighters/rogues/archers fare, but in terms of spells, you either need to significantly buff magic or increase the number of available skill points. This isn't just my opinion.
Well, I think you planned that once people start creating characters, you can adjust the balance, so it's not a big deal.