ok, maybe they do need to be more powerful, but not much, comparing max hp and regular hp is not a good idea.
regular hp has lots of opportunities to regenerate each turn, 23 creatures time 6 feral bonds is what, 138 hp per turn. but you can be taking hundred of hp in damage a turn too, a few chargers etc.
max hp is a limit, not a value. once you start getting reduced all that healing is gone. 670 max hp, usually cant be reached until late mid game if ever. there are 2 cards that raise max hp.
SoD, 20 for 3 other once, so 6 hp per quanta. but its single use it should be pretty good.
right now this has the potential to be raising max hp by 18 ,my original upped card was +4 so 24 if all 6 i lowered it because the last few cards i made i was told were too strong i was trying to tone it down, anyway, 18 max hp if you have 6 is like playing a SoD every turn. its nearly +100 max hp every five turns. it takes usually ten turns or more to get 75 from granite skin, and then you can play all of them, but then you cant raise anymore.
eternity, rol, these and you can have unlimited max hp, i dont want to make it too strong. it was 9
to get 3 and 8
to get 4.
5 hp each per turn times all 6 is 30 max hp or 300 max hp every 10 turns. that is overpowered.