I would say that there is no weakness for the noct AST
Because if indom is great for an emergency heal
The AST can just helios and do the same... Plus helios do not have 30sec CD unlike indom

Plus if you lightspeed it it's super strong and you can make the whm cry in a corner.
(Lightspeed got a medium cooldown duration that make it useable many time in the fight
(Enhanced spire can make it down to 1min CD !)