Astro base heal costs less than Scholar base heal.
Astro group heal has the 150% heal potency for barriers, Scholar doesn't at the moment and scholar's costs more.
Astro has constant instant cast heal spells while Scholar has to use stacks in order to use instants.
Astro has all around cheaper spell costs.

And when I was leveling Astro, compared to when I was leveling Scholar, Scholar had way more MP issues than Astro did. It was pretty easy to heal as Ast/Whm compared to it, even more so with bigger pulls.