Just fought it and I found a way to cheese the fight on 1st try.
I’m playing necro minion build with Bone golem that has the threat increased node.
So once I aggroed Harkon I just run on the far right of the area so that only one Idol of ruin and Harkon are on screen. This put the other idol of ruin purely out of the fight until the end.
Then once I’ve lured him there I just positionned behind Harkon and now I’m out of danger until the end of the fight as my bone golem is the only focus of the idol and Harkon.
After that the fight was following this plan : dread shade - > wait -> one minion down -> resummon -> rinse and repeat until the end.
I don’t know if such a cheese can be done in the empowered version of the encouter though. If yes then maybe some tweaks could be done to make such cheese impossible.
The 2 idols idea is good, maybe could changed a bit to prevent such cheese. Would be interesting to have mutliple holes in the area where the 2 idols could pop out like a wack-a-mole forcing you to reposition at some point so that such cheese could not be possible.