7 Combos is definitely good enough.
What does your team look like? You're going to need some short cd orb changers here to kill Raphael and get them back up for Sandalphon again. (You don't happen to have a dark monster on the team... right?)
Sandalphon changes your dark to light orbs 70% of the time, so it helps you do more combos and clear away orbs for more chances of heart orbs dropping, but you'll have to make sure your hp and rcv is high enough, since you'll have to be stalling for at least 5 turns.
Actually, you might need to worry about accidentally dropping him under 50% and him binding all your gods.
I actually bring an Amaterasu with me when doing Sandalphon because I keep accidentally getting 10 turn binded.
As a non-iap player, I generally don't recommend using stones for continues when you can definitely do better if you tried again after a month or two.
Sandalphon's definitely not an easy Mythical, though not the hardest ones.
Because I'm in the dungeon still I can't check my exact stats, but this is roughly my team:
Blue Valkyrie (max level, ~+180)
Echidna (level 96)
Siren (~level 70, max skillups)
Archangel (the blue/white one, ~level 80)
King Shynee (Max level)
I&I friend (Max level, +297)
Everything ultimate evolved and fully awoken, no skillups at all aside from Siren. No dark monster.
Once again I can see how having Valkyrie and Echidna skillmaxed would be a HUGE help here, but the one day since I had a good enough team to actually farm Valkyrie skillups when they were available was a day when I had trouble getting helpers for it (since it was a rarity-restricted dungeon), only dropped a couple, and got nothing from them. Until Poring Tower comes back or we get the Naga dungeon I can't do anything about that at all. And my success rate for skillups so far has been beyond abysmal (I've been trying to get a skillmaxed Rowdy Samurai Goblin for Tengu, and so far my record is
1/35), so even those might not do anything.
I suspect Archangel isn't really good enough to be on this team, but I can't think of a readily available non-REM replacement for her. That team spot really,
really wants Amaterasu, Metatron, or Ceres in it but I don't have them and probably won't.
I'll probably let Raphael kill me eventually. I've been trying to figure out what my odds of being able to keep up my healing against Sandy are, but I really have no way to deal with him once I&I gets bound, so the 1-2 stones it will take me to even get that far definitely aren't worth it. Wasted 100 stamina on this dungeon today which isn't great (got orbtrolled against the Unicorns the first time), but at least I learned something sort of. And got some good combo practice I guess.