@Valorian
Absolutely not, it's like saying doing side quest promotes a play style over the others. You can choose as a player to explore the world whether or not you tend to rely to fighting or sneaking to resolve problems.
I'm afraid i'm not making myself clear, of course you WILL receive xp for wiping out a group of cultist for exemple, but you will gain that xp as part of a bigger goal "getting rid of the cult" not a few points at a time, cultist after cultist, just like a more diplomatic player won't get xp after each npc he convinces. In the end for the "fighting style" it doesn't matter how the xp is distributed.
It's just that the guy snicking up and making the ritual go all wrong buy removing a regent will have the same xp, because he will also have "delt with the cult" but in a different way. The snicking and lock-picking will not reward points in and of themselves, just like every cultist did not gave you xp.
Again, i'm not saying "you should not fight and be rewarded for it" i'm just saying rewarding for accomplishing goals, whatever the way you choose to use, would be great. And if a matter can only be dealt with buy hacking and slashing then give the reward after the fight for "dealing with/surviving the bandit ambush". I'm good with it.