Hard to say without watching how you guys were fighting it, and what role you are, but if by ground AoEs you mean the tiny ones Talen-Lah shoots when he's walking forward, it's easy to avoid them.

Before he starts walking and casting them you can see a telegraph showing exactly to what direction he'll walk to, he always shoots them sideways and by the end of the telegraph he will stop and shoot another few forward.

All you need to do to safely avoid them is to just walk to the end of the telegraph before he actually starts casting the AoEs, that way you'll be safe from most of them and the last few you can just dodge through, this always works, but keep an eye on the behemoth, he might bonk you behind your back as you do this.

If you're talking about Dirge though, which is the mechanic where Talen summons 2 mages that create big circles around them, you need at least one person standing on each of the circles, if you don't, they'll start doing some heavy damage on everyone, though I'm not sure how heavy it is on non-HM.

There are several other details I could go on about, but it would be too long, you could watch a video of other groups running it.