For Valeska at level 20, we will have a bonus of +3 attack and +2 defense
For Orrin at level 20 with expert Archery, the bonus will be +50%(1+0.05*20)=+100% damage. Which is clearly better!
The screenshots show damage against peasants and against each other (due to Valeska's defense bonus being higher, the formula used in the calculation is different). Both heroes have expert Archery and combat stats of 9/9
Valeska's plus is that she has +1 speed and outruns many monsters (griffins in the Griffin Conservatory for example), while Orrin's plus is that his specialty works on all shooters. Valeska's minus is that you might be short on archers from the start, but the plus is that you might get more :D
P.S.: Note an interesting fact: the peasants are in two stacks against Valeska, but in three stacks against Orrin, therefore Valeska is more respected ;)