Battle frenzy and Vitality cannot be compared as a plain statistics because Defense is better than Offense anytime.

50% defense > 50% offense because 50% defense is half the damage while twice the damage is 100% offense.

In regards to the 15% bonus health - this is a skill I would pick anytime this is ~ 30HP boost for tier 7 units. "stand your ground" and "power of stone" cannot be equal unless the numbers are as high as the sky. Also from the Defense skill picture it seems the player can pick both "Vitality" and +15% hit points which is even more absurd.

What are the numbers for the other skills in Defense tree?

@Nargott I am going away for some time I want to get to know the wheel structure before saying anything more. May be I do not understand the idea correctly.

Cheers