I find your system quite interesting. Thanks for sharing!

I was looking at the Violence section, and (it seems to me that) stats do not help much to defend better. 

For instance, if I understand the rules correctly, here are all possible amounts of damage an adventurer with 11 agility could receive when trying to evade a hit: 

Expected damage: 9.95

And here's the same for an adventurer with 18 agility:

Expected damage: 9.6

Am I understanding correctly? Also, is it impossible for a character to completely avoid damage?

Thanks in advance for your clarification!

You're understanding correctly. Combat is a failure state and should be avoided. You're made of meat and when you get hit you bleed and die.

I updated the PDF today to add that if you roll exactly your stay when defending you don't take damage. You've shown this on your charts - the results for 11 on the first chart and 18 on the second one show 0 damage.

Thanks for the clarification!