Instead of posting the same again, i will just post the link here to my original post @ PTR forum:
I think their rotation is fine. What I would like to see is instead of Ice Lance and Glacial Spike cleaving, I think instead when a spell is Shattered it causes shards of ice to erupt from your target and hit enemies around them. This is a fantasy that Path of Exile leans into with a number of their frost abilities and it’s very gratifying to make frozen enemies explode in that game.
I’d rather see the cleaving ability improved for Frostbolt (i.e. making a dedicated Frostbolt ‘cleave’ build).
This was kind of already in the game in Shadowlands with the legendary power Glacial Fragments - Spell - World of Warcraft. I prefer the cleave we get from Splitting Ice personally though, but this legendary being made into a talent wouldn’t have upset me.