My own take on it right now is that AST suffers too much in its basic heals in return for very circumstantially useful buffs. It results in a number of "if this and this and this happen, then using the cards this way was worth it". For example getting Spear card just as someone is about to trigger several abilities with cooldowns, or Bole before a big boss hit, or Spire on someone who would have ran out of TP if you had not used Spire. And the more times you spend redrawing to fish a good card, the less useful it is overall.

Take a best-case and always-useful scenario where you royal road Arrow or Spear, then draw Balance or Arrow, for raid dps. You increase raid dps by 5% for 15 seconds, at the cost of two draws, so once a minute. This works out to 1.25% dps to the raid. This also only has an 11% chance to actually happen, without using additional abilities like spread and shuffle. Compare this to Selene, a pet, who offers 3% speed with 50% uptime, and works 100% of the time. So about 1.5% bonus dps.