Writing on the official boards, Greshowitz explained the way offensive and defensive stats “comepe” against each other:
For example, if a Bright Wizard with 900 INT attacks a Chosen with 500 Toughness, the attack bonus is 400. If a Chosen with 600 STR attacks a Bright Wizard with 200 toughness, the attack bonus would be 400. As you can see, they both have the same bonus, the only difference being the way the bonus applies to the attacks.
You can read more following the link I gave you, but the conclusion is as follows:
“So as you can see it is our goal to make stats effect abilities relatively evenly regardless of the type of attack. Thus having high Attack stats don’t necessarily make your weakest abilities hit like trucks. In addition we want to make sure that players recognize the value inherent to taking some toughness into their builds, since it can be as valuable (or more valuable) then armor or resistances in many cases.”