How does leveling affect stats?

[Kwal]

I wouldnt be so sure about the modding. I believe all the stats and skills are hard coded and you cant just give them a new effect, not without WSE at least.
Also, saying that AGI increases weapon speed because it gives you weapon points that you can invest into one of the proficiency is like saying STR increases your damage with bows/throwing weapons, because you can invest the skill point into that particular skill.

I said indirectly, so yea.