Comparing WHM and AST, you'll see that it's more about tweaks to the general concept of healing in FFXIV. You don't need to constantly heal, you have DPS spells and abilities that you must use. AST will bring in the cards and introduce the buffing system as part of your tool kit. Once you reach level 50 with AST you will have access to Nocturnal Sect, which will introduce you to the other side of healing which is shielding (pre-emptive healing for damage mitigation). That's another way of healing, but once you get the general idea of Regen vs Shielding, you're pretty much ready to heal anything in FFXIV.

And I'll say it again as previously said, don't worry about healer balance. You're not in high end content yet, and it wil most likely change with 5.0 Shadowbringers in 6 -7 months. Enjoy the game at your own pace, with the jobs you feel like trying.