You keep saying you can add more vit to your build to get an equal amount of hp as a skull cap. On the other hand, if you increase the base vit with the skull cap build by the same amount of vit you're left in the same position so the argument is a wash.
I know the percentage change in HP. My point isn't that the hat itself will imbalance everything. My point IS that we can't keep increasing HP modifiers. Balloon, cape, and now halloween helmets are all boosting up HP rates. (It is my theory that this was done to counter act the tao gunka "fix" a few months back)
If we keep following this path of just buffing HP we're going to have classes become very imbalanced. The classes I mentioned (sinx, pala, LK) have huge HP modifiers. If we keep popping off HP % increases these classes will get close to being unkillable outside of coma and that my friend is not balanced. I saw a sinx and a paladin tanking aproximately 15-18 people in WoE yesterday for a solid 2-2.5 minutes. The last thing I think we need to do is give them more HP.
Classes who don't need buffs, like the above mentioned, will be getting a greater gain off of this change than those who actually need it (Clown/SG/Wiz/Prof). Too many flat percentage HP boosts across the class board are imbalanced because all the classes have different HP modifiers. Some classes do need more HP, but a lot of them do not.
I agree that changing 15% to 20% won't break the game but it's a slippery slope to things that WILL later on. Just like how we started stacking all the demi-human reductions in the past.
Lastly, I've said this before: I've seen people ingame using the hats. They serve a purpose already, whether it be cosmetic or otherwise.