Only that AST isn't complex. It's bloated with buttons that have very similiar effects on a similiar cooldown, highly mobile, doesn't have to worry about weaving and has one dot and one filler.
Don't mistake the amount of buttons for complexity.
And that's exactly what's turning many players off: lots of buttons but nothing behind them. At the same time, classes like DNC, RDM, DRG and BLM often get praises for great, fluent and fun gameplay while not having their hotbars bloated with meaningless busywork.
So asking for a specific amount of buttons doesn't make sense, certainly not for all classes across the board. They don't need to add more buttons to add new and fresh mechanics to classes. Just because you want more buttons for your MCH doesn't mean all classes should get the same treatment and streamlined when it comes to a metric that doesn't mean anything in terms of complexity or fun gameplay.