ehh 20 runs for MAYBE one Hp+15%
you basically have to be committed to farming this event and the unit XP sucks since youll likely need a strong ass team to beat the bosses
Both bosses spawn in the same place. They either drop 0-2(I have yet to get either not to drop, so I'm not sure about the 0), so you're averaging a bit better than 1 per go.
You need 20 Pearls from the Siren for the HP and 20 Powder combined for both the other 2 from the Golem.
So you run this 15 times, you'll have all 3. If you choose to do this for your daily Vortex. You'll have enough mats in 5 days.
So no, it's not 20 runs for maybe the 15+HP. By 20, you should have it.
And that is if you are only focusing on it, which I think is fairly short sighted.
This vortex has a lot going for it.
1. Exp is around 70k per run. You are netting the same as an Int Vortex for each character. (Throw 1 or 2 ones you're still leveling up on, or one if you don't care about it dying).
2. The drop rate for Earth Megacrystals are very high. You need 20x for every Monarch Ring. These are the next step up from the Hero Ring. Farm now while they are dropping at a great rate.
3. An additional Turtles and Cati you get are bonuses. I.E. a free 15k or 30k Exp. You'll typically run into one each turn.
4. Other rare materials like Mylthril Ore, Heaven's Ash, and others drop with a decent rate here.
It's no different when people fixate on pulling one character rather than the overall picture. This is a fairly good dungeon with a solid upgrade(15% HP) and lots of additional benefits. Basically you are running an Adv Exp, Adv Awakening, Adv Material at the same time as having an exploration map with 5 Resource nodes.
I feel like this is just you wanting the quick fix and be done with it. When really, running this dungeon once is equal to about 60 energy used for 4 other different things.