Some important things you're missing that helped our team beat it on hard in 3 runs even with a level 28 on our team and no Titans. 1) Those OUTSIDE of the portal open the proper portal and then IMMEDIATELY run to the middle platform and start clearing out harpies from the MIDDLE. Harpies cannot close the portal and they also cannot cross over the center platform. (ie; they cannot blow you up) What this does is make it so the 3 people outside are already in the middle ready to unload on Atheon the second the relic holder gets there. 2) If people inside of the portal are having trouble killing oracles, ONE of the people OUTSIDE of the portal can run into the portal and help with the last few Oracles. Have those inside call out when they need help, then that person can just join the "run" to the middle with the relic holder and other 2 players. These are what helped us crush Atheon pretty easily combined with the other stuff you mentioned which we were already doing.