Puppy, as you may notice rereading my post, I just pointed a finger at the card, I didnt offer any solution to the problem. Not very constructive, I know, but as you already said yourself, none of the cards on their own is so terribly overpowered. And I generally agree with that statement.
I do consider SoGs too strong in combinations with other cards, but I'm aware that having negative opinion on popular cards is... not popular.
And this very combination - of element that has the most powerful destruction and damage cards, and generally good healing (I think we can all agree that SoGs indeed ARE powerfull as they can be put in almost every deck) is simply (too) strong.
I'm fairly certain many decks could kill fire stall without healing. There are creatures you wont be able to touch with your CC (immortal creatures, burrow creatures), there are creatures that require multiple CC to be taken off the field, there are other types of damage (spell damage, poison). And then, there's draw. You really dont have to have 100 dmg in total to take down firestall that doesnt use SoGs. Firestall becomes MUCH more vulnerable without them.
I'm not saying removing SoGs means everything beats that deck, I'm saying that the deck itself wouldnt be nearly as OP as it is considered now.
But yeah, SoG is here to stay. So pointing fingers without providing a solution doesnt do us much good.
As for your comparison with Sundial, I agree with your facts you make there, but I disagree with conclusion. We already established that SoG on its own isnt such an awesome i-win card. It becomes great when spamed and/or combined with shields/CC. Sundial had the same power level regardless of other cards; it always provided no attack for 2 turns and drawing power. SoGs always provide 5xN healing, but healing per turn must be looked through damage per turn you receive. If you're healing for 20, but receiving 30 damage per turn, your HP bar goes down. If you're healing for 20, but receiving 10 per turn, your HP bar goes up. Big difference.
Anyway, point I'm trying to make is that every buff/nerf/rework must be looked seperately. You cant just draw conclusion: "if this card was buffed/nerfed by that much, than this card shouldnt be buffed/nerfed by this much".
After all that said, I'm not even sure myself what I'd do here. I also like to use SoGs in my decks, and dont think they should be removed from the game. However, in elements setup where every element has a field where it dominates, having a card that provides something powerful like healing to ALL elements is... well, tricky
Suddenly you cant just say "its ok for fire to have massive damage and control, their defence sucks".
Other "other" cards either provide damage (that every element already has), or makes playing their strenghts easier (SoR). SoGs (and SoDs, but overall those are just weaker), give something NEW to all elements.
Maybe something along the lines of weapons that have extra benefit when combined with some elements, could be used on SoGs too.