I'm fairly new to AST; with it now being my main cuz I fell in love with it due to the card/buffing system and how stunning all the spells and abilities look. Specially compared to how lackluster/ordinary WHM and SCH abilities/spells look. Going back to your original post, you mentioned that you were going to have to switch because you needed a shield healer since your friend goes WHM; but I've always read/seen that Diurnal Sect should always be your go to choice when playing AST and that you should really only ever use Diurnal when playing with another AST. So you should still be able to play AST just fine.