I’m guessing the damage is lower due to the persistent damage and the fact that spirit damage can take effect if the target has fire resistance/immunity.

Spirit damage is a new damage type that replaces the law/chaos alignment damage. There was also a leaked sidebar from Rage of Elements which has the following:

Vitality and void replace positive and negative traits and damage.

I presume this is due to positive/negative being OGL terms.

“I am totally normal human!”

I feel like there would be a speed penalty for being large and that possibly they might remove reach as a benefit of Large for those ancestries. But I have no idea how close my thoughts are to what they would do.