Finally, my team is good enough to clear Hera without the need of a resolve leader as long as I get a good Odin from my friends.
Here's my team with an ally's Odin as leader.
The most important thing is to get the HP above 16500. Secondly, it's best to have a strong AOE nuker. Machine dragons fits the bill nicely with their decent atk, 30k nukes and high HP. Since I didn't get light and dark machine dragons back then, I used water as it complements nicely with Neptune and prevents splitting up the elements even further.
Play is standard. Store gems so that you can chain combos and AOE on next turn, make sure your AOE skill is up and ready and you are set. Odin's skill provides additional coverage, really useful.
The most painful stage, but not that much of a big deal when it has a 6 turns cooldown and my Amaterasu can heal the missing HP within 5 turns.
Hera deals 2471dmg with Odin's skill. Ouch.
Even with a slip of the finger, I can still tank through her second blow. Amaterasu for full heal and I am set to go again.
It takes me 1 hour to get the egg this time. Much less stressful compared to my first attempt, faster and no luck involved. It's almost a definite egg get as long as I do not do something stupid.