I'd say keep the entrance part, but remove the volcano. We've seen several artistic images of Kurgans, at least temporarily, having an entrance.
For the stele, I think they should have a more regular pattern to their layout.
For the rocks along the base, I think they look too chaotic right now. I agree there needs to be something to help the hill of the kurgan to blend with the existing terrain mesh and rocks are a good way to do it, it's just too chaotic looking right now. You are on the right track. I appreciate the attempt at some detail at the top, but in no reference or even artistic interpretation have I seen a pile of rocks at the top, though I am open to being wrong. You did a really good job UV mapping the grass on the hillside. Most of the other attempts from other artists have kinda failed at this detail. I appreciate the effort and would really like to see you keep iterating on this and making something nice. I'd also like it if you made a 2nd custom mesh for its foundation actor too, because as you've noted, it's quite a different construction from other buildings in the game.