No. I've raided as a Noct AST and with multiple SCH's who are always on top of their game and know what's going on. I'm quite familiar with the tools because I have a pocket SCH when I tank, and we work out how to do our best as a pair. SCH was designed from the ground up to mitigate; AST was not. It's not rocket surgery to see that SCH's kit is far better for that role.
I've PvPed as Noct AST a handful of times in the drought before 3.1 when I really didn't want to get Neverreap again. You're right, it is extremely powerful. I'm not all that knowledgeable on PvP though, but my thought is that PvP would need a lot of tweaking to be a well-balanced experience.
I do agree that they're more equivalent in 2.X content, but I don't think that should be a major contributing factor when it comes to discussing its balance. It's nice, but AST is a HW job, so talking about its usefulness in ARR seems a bit tangential to me. I doubt many people are going to hit HW specifically because they want to heal ARR content as an AST and as no other healing job, and the only way they'd get non-faceroll content otherwise is by doing min ilvl sync.
As far as progression goes, SCH DPS is definitely an important factor, but AST could have the ability to contribute in a harder to calculate way. An AoE balance is an incredible boon, but it's not as easy to calculate how that contributes to the raid's DPS as it is to look at a SCH's potencies. I'm sure it's doable, but as it stands right now, your raidwide DPS contribution comes from having an Expanded Balance Spread at the start of the pull. Beyond that, you're stuck with a weaker WHM for DPS and RNG for your other contributions, including enough MP regen to keep yourself on track with WHM. If healer DPS is truly a problem, having the equivalent of an Expanded card without needing to burn a Spire or Ewer would significantly increase the frequency of cards played and boost raid damage more. An AST feeding one person cards is great for their personal DPS, but this way they could increase their raidwide contribution without having to wait ages for a Balance or Arrow.
As far as overestimating the fairy goes, you're probably right. I know fairy heals aren't as strong as SCH heals, but even if your fairy is set to manual and you never use a single pet ability, it's going to ease your healing burden because it will always be healing.
I probably forgot to address some things but oh well.
I was poking fun at myself, because I'm aware it doesn't resemble anything close to balanced, proper, or reasonable. I just wanna kick my ideas around a bit.