Isn't that why we divided Guts into three different versions, though? Before DS, After DS, After Berserk Armor. They all have different stats.
It's kinda like making different versions for characters like Saber/Emiya with different weapons. Remove weapons from them and they would be much weaker, but in most VS battles we already assume that most characters have their standard gear.
As for Skull Knight AP, we can still try using the energy output of a tornado. We can scale them to natural tornadoes after getting the diameter of the tornado.
http://www.dailymail.co.uk/news/art...600-TIMES-powerful-Hiroshima-atomic-bomb.html
Bigger than Hiroshima: Monster tornado measuring 17 miles long and 1.3 miles wide was 600 TIMES more powerful than atomic bomb as NASA releases images of twister from space
1.3 miles is 2.1 km, so if we get the diameter for the tornado in that scene, we can use inverse square law for the energy.
I'll assume 105 m diameter for convenience, and same wind speed.
2.1 km / 0.105 km * 600 times = 30 times
Square root of 30 times = 5.47722557505
5.47722557505 * 20 kilotons = 109.544511501 kilotons
That's High 7-C Large Town level.
Generally distinctly supernatural feats (with lightning shown inside that small tornado; we just don't know how much energy those lightning have) are considered >= natural feats, so that's just the minimal energy.
We only need to get the diameter via pixel scaling to determine the affected area.
And it seems the compared tornado was still 1.5 times weaker than the one with the highest wind speed (200-210 mph vs 302 mph). A peak tornado that occurs on Earth would have 1.5 times that energy for the same size. That may be used for the high end, though it's still the same tier.
Essentially we would be getting SK and Zodd's durability, when they are caught in the same tornado, and scale their AP from there for their ability to damage each other.
If they check in then they could be At Least 7-C (from tornado feat) to Likely Low 7-B (from Shiva stomp feat).