I wish more like you would chime in. I have no idea about any MCH abilities and am always confused who to give spear to. I also see conflicting crap on Reddit in regards to which classes desire which cards.
I know on BLM, I personally prefer arrow over anything else. It allows you to do 3 F4 for every F1 opposed to 2 F4 for every F1 as well as a whole bunch of other awesome stuff. But I also see a lot of people advocating for melee to get arrow. I understand it in MNK's case as it allows them to ramp up faster if they don't have PB up but I still think it benefits BLM the most if given at the right time.
I'm also tending to cancel expanded RR more often than not that comes from spear. Unless it's an expanded balance, I just don't see the benefit for the others at half potency.
After leveling all three healers to 60, AST is really lacking in solo play but very nice in group play. The tweaks will make it so much more fun to play but there are still things that just don't make sense. CU is poorly thought out and impractical, synastry's CD is too long, CO seems lacking. I at least think the extended buff portion should be extended to 10 seconds. I think spear should be retroactive but I highly doubt that will ever be implemented. Ewer and Spire should regenerate MP/TP instead of cutting the cost. Each card's duration should probably be tweaked a little as well.
You're also really punished for DPSing on AST compared to the other two despite AST having some very nice DPS capabilities in both group play and raid content where accuracy is an issue. I feel that gravity should probably apply a slow to the target to mimic shadowflare. People don't seem to grasp just how big 5% slow is on shadowflare in terms of mitigation and ability to DPS longer before having to heal.
I leveled WHM right next to AST and the difference between the two was disturbing. As WHM, especially post 58, I could easily pull SCH-like numbers on AoE pulls without running out of MP. Stun offers mitigation and aero 3 gave a much needed AoE DoT. I could easily DS + regen/asylum and not have to heal at all. On AST, there really is no safe window. You gravity till the tank is about to die, hop out and ED. At that point, you really have no other options to continue DPSing. It's a detriment to do so since your MP regeneration is crap. I've had to completely stop on bosses at certain points because I just couldn't keep up with the cost of combust II and combust.
I don't think healing potency necessarily needs to be fixed. If we're supposed to be the super efficient class with weaker heals, we need an edge on MP efficiency in other areas. Heck, making Ewer regenerate MP alone would give us this edge.