According to FFLogs, AST pDPS >= WHM pDPS in 4.3

[Caduagm]

I agree with everything you're saying here, except this bit.
It's a bit of a stretch to say WHM feels fluid. All of their OGCD heals will clip into their GCD, that goes from DPSing with Assize to putting down Asylum.

What do you mean by that? Are you really comparing the 6 oGCDs WHM has to the 15 ones AST does? Please, don't make me laugh.
You have Aero II with a very small DoT time to weave these oGCDs.

I also think Medica II needs to be brought down to 2.5 seconds as well, as it just feels like a completely unnecessary cast time that does nothing but further widen the DPS gap between healers.

No. Medica II is the strongest GCD AoE based regen in this game, with a larger range.
The changes to Aspected Helios was to be on par with Scholar.

These have always been issues, but I feel it's a lot more noticeable now that AST and SCH has had such nice QoL given to them.

Don' t start victmizing WHM. They got very good QoL changes too. Plenary Indulgence and Divine Benison are good examples.