For AST changes, just potency buff malefic and combust...

[DaFood]

At the highest levels, AST is relatively competitive in terms of rDPS with the other two healers—and rDPS is the only metric that matters. Sure, it lags behind by ~500 at 95th percentile (~800 at Max), but I don’t think that’s what’s holding it back. I’d wager that what’s holding AST back is the gameplay: the new card system is heavily divisive between the players that love it and ones that hate it. AST has to do twice the work in their openers and general rotations to achieve the same results as a WHM—WHM has its issues, but it feels far more fluid than AST does. Honestly, the current design of AST is why I’m no longer playing it.

I don’t think potency buffs alone would cause us to see this sudden influx of AST players and make it directly competitive in numbers with WHM and SCH. NIN got potency buffs, but it’s still one of the more underrepresented DPS jobs despite doing comparable damage to the other melee DPS now (this is from it being one of the Top 3 most popular jobs—and one of the staple meta jobs—since its inception). Why? Because people don’t like the gameplay—and its gameplay is actually getting addressed in Patch 5.1.

I know simple potency buff won't be enough for current situation because it will at least serve as a band-aid.
I will be amused if you think that 500~800 difference is small enough to ignore it.

If AST get potency buffed, WHM's population will slightly shift to AST. But there will still be decent amount of population playing whm because that class is easy to play and that's what WHM is design for right from the beginning.