The HP of those ice turrets are beyond those who have moved to higher tiers. I used to be able to clear them with spells, swap riders and use of dragons with different strength that complement one another. But this is going nowhere since I have progressed and removed runes for my empyrean and now harbinger is too weak for those towers.
I’m not going to waste energy or swap in riders or plug in new runes just for the challenge and this is ridiculous. PG should do some adjustment as this cannot be a one size fit all centre guardians. By the way why not set all the HP of the ice turrets to be infinite and that will definitely be serving the challenge and a money drain for energy and other resources? Can’t think of a better sarcasm