I've beaten it twice with my group before, but for whatever reason, we're struggling even more so than the first time.
I'm 29 and everyone else is 26 or 27. We've probably been at Atheon for 2 hours. Absolutely ridiculous.
The likely culprit is people skimping because of confidence. I'd say that whoever your raid leader is (likely you) should be making sure that communication is adequate. Before you start your next attempt, just reiterate who's going where, when, and why. For example, mine is composed of A, B, C, D, E, F, and G (myself). I'd say, "okay, so why are we placing who we are, where we are?" In my groups case, we send our Striker Titan in to grab the relic, along with myself (going as a Gunslinger Hunter) and a third (this varies, but generally a Defender Titan) into the portals. We keep two Sunbro's and a Gunbro protecting the portals from outside, because they have the hard job. The Sunbro's being able to self-res stops potential wipes, and the Gunbro's super is good at cleaning up the Harpies relatively quickly.
The big reason, though, that we have those 3 outside is that they're all fans of semi-auto weapons, which are best for precision kills but not good against the oracles due to sheer DPS needed. So, I go into the portal with an auto-rifle so that we can quickly clean up the oracles, and keep consistent damage on the boss. While harpies are clear on the outside, they put precision damage and grenade damage on the boss (worth noting grenade damage is not impacted whatsoever, so it always does full damage no matter what). Also, whoever has the relic should be calling out for help if they need it. Granted, the only thing that is a relative problem is the Minotaur in the Jungle portal, but I'll use my Gunslinger Super as soon as we get in so that it goes down in the first hit or two. When I forget to do that, we have more wipes than I'd like to admit.
Other than that, if you're struggling, try and figure out which side is having problems. For a while we had trouble on the outside because we were trying to protect both portals. We eventually figured out it's easier to just protect one, and then have the portal group call which one they're in so that they know which one to protect.