What i don't like about your system is that it has most impact on the start of the game and less later. The difference between 1 attribute point when you have 4 or 5 is large. Whether you have 13 or 14 is a small difference. So your system doesn't scale. I also don't like the idea of starting with very little AP, as fights are hard enough in the beginning, and it's a non-fun penalty. Add to that the chance of fumbling spells, it would be all about getting certain attributes to 8,so that you can actually start to play. And from there make less and less difference.
One thing which is a little odd about D:OS is its early game difficulty. Usually you can expect difficulty in a game to ramp up over time, and it often seems like this isn't the case in D:OS. Thus, the rebalancing of some encounters would be necessary for my system
such as the 2nd/3rd fight when the orcs land on the beach
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