I've yet to play truly challenging 8 man content, but in the few 8 mans I've played, most healers don't really know how to react to Astrologian. They tend to act as though you are the WHM to their SCH, or vice versa, or ignore you entirely, but I don't think AST will be able to shine like that. They simply don't have the specialization. I feel that AST should act to cover the other healer's blind spots, while they work to cover AST's.

The WHM/AST dynamic seems fairly straightforward, WHM healing like they do best, with AST buffing and DPS'ing, stepping in to mitigate and spot heal. AST/SCH seems fuzzy, but I'm curious to see how they work if they meet halfway. AST needs some help to deal with burst healing, which brings up complaints about SCH's DPS uptime, but you end up with two healers that can buff the party in myriad ways and apply high potency DoT's without the need for accuracy to compensate. I'd need to spend some time with coordinated players to really feel out the dynamics of full party play.

That puts AST in a tricky position, because it benefits the most from interacting with the other healer. WHM and SCH act more as separate entities working towards the same goal, whereas AST seeks to cooperate with the other. This isn't inherently a bad thing, except for the fact that, if your co-healer goes down, you'll find yourself in a tight spot very fast if they can't be revived in time for important mechanics. I'll withhold my judgement for now, not having much first hand experience, but I still find AST to be a lot of fun to play, and don't plan on quitting it any time soon.