AST low DPS overblown?

No, it's not overblown. Head over to FFlogs, pick a fight, and look at all the healers. AST is always the lowest by a significant margin. Their personal DPS is the weakest in the game. The exact amount varies by which encounter you look at, but it's pretty much always at least 25% (and seems to be even higher in Rabanastre, which could be due to who is doing that regularly vs savage). It doesn't tend to matter as much in group content because cards and they can push a lot of HPS.

But I find playing AST outdoors downright painful.

It's down to the fact AST is fundamentally the closest to a support job we have in FFXIV.

So many skills are dedicated towards the card system that an AST only has the single most basic damaging spells, but more than makes up the output difference by properly buffing allies in group content.

It's fine.