Purify is not a viable alternative to SoG unless you simply can't afford or don't have SoGs. Shards are the best early-game healing, and they're not expensive (in terms of quanta). Most FG decks have 4-6 SoGs in them, along with a couple shields and weapons, so having all of your SoG destroyed or stolen usually isn't a problem unless the god has a pulverizer or its Rainbow. If you put out 4 SoGs and have 2 stolen, you're still going to be healing as much as 5 purifys. Best situation, purify is healing 12 at the end of the game vs 30 for SoGs. I'd still take Feral Bonds over purify for main healing in a deck, except that they require creatures and generally fit into a large rainbow. Anyways, the 2 extra healing is just a buff to the otherwise useless purify, it's not going to make it a suddenly overpowered card.
edit** This belongs in general discussion, not in the decks section