Math is just ...Math. The thing are:
1) u only get the bonus from Fire Mastery when u use spell. Later chapter more than 10 active spells and Galeoth is a real spell caster, u will not use Phodom's spells that much, believe me.
2) With Heaven's Bless, i even don't need any healing spells as well as potions.
3) For me, Phodom is a tanker and Aura of Fire is just great for his tank. I would love to see him with Aura of Fire, Silver Set and Red Orb set, he would kill every single normal monsters without using spells or even physical attack
Just my opinion
1) That is true.
2) Wait, Heaven's Bless is a spell isn't it? =O
Mocking over, anyway if I'm reading Heaven's Bless correctly, it heals 549.44 (with my stated stats including the magbonus %) or revive with 55% hp and 10% mana. That Vs 1088 health. Thats still almost double. Not to mention, thats 1088 every 10 secs, vs 549.44 every 12 seconds. Going on not needing healing spells, its not much of a heal compared to shield of fire. But comparing shield of fire to the revive, different story. (in which case, Heaven's Bless would win 9 times out of 10)
3) Yes he's a tanker, thats the main reason for shield of fire, other wise I would go Heaven's Bless. I'd rather not give a risk to my dps (Galeoth) because Phodom died and is waiting to come back to life. Which, by the time Galeorth dies, the buff is over, thus he dies and doesn't come back. (again, that is if I reading it correctly, it doesn't say the revive is instant, and it doesn't say that its not instant.)
4) I'm not planning for normal monsters. Planning for the elite, and epic bosses. In every RPG I've seen, higher HPS is better than something like reincarnation. Why? Because then the tank lasts longer, and there isn't that wait time to the hero to revive, which can cost the game. On the other hand, reincarnation is good, if you have more than 1 tank. That why while 1 tank is waiting to revive, the other can take over for a bit, thus reassuring that your squishy heroes are not in any danger.
5) If the revive is instant, then every spell on Phodom is useless aside from Heaven's Bless. Aura of fire, or shield of fire, it wouldn't matter.