All my jobs fit on this with at least eight slots open. That is to say, any job should be able to fit on three hotbars.
Most actions are on 1-6 with four possible modifiers. I avoid binding anything to Sh+6 or ASh+6 because they're just too easy to get wrong when everything is happening quickly.
On healers I don't use the the top Sh1-Sh6 and ASh1-Ash6 rows (UI Hotbar 2) except to show cooldowns. Most heals are bound to the mouse cluster (UI Hotbar 3), which uses middle click, navForward, and navBack.
The navigation cluster (UI Hotbar 4) has Sprint on Del and knockback blocker on End for all jobs. Jobs that have gap closers use Ins and jobs with backsteps use Home. Sprint and knockback blocker are also bound to thumb buttons on mouse in case I'm healing.
I don't play with a mouse unless I'm healing. My resting hand position is left hand thumb on alt, ring finger on 1/A, index on 3/D. Right hand thumb on ctrl, fingers on arrows/nav. Target Nearest Enemy is G/backslash and duty action is X/rightbracket so either hand can press either button quickly. I access the ASh row with left thumb alt and right index shift, except when healing since I mouseover heal; in that case I access my ASh heals with left thumb alt, left pinky shift.
Not pictured are the limit break button, which is bound to CASh+L so if I press it it's very deliberate. Also not pictured is a hotbar to the left of the party list with buttons lined up with party slots for direct macroed things like Aetherial Manipulation or Rescue on each party member; these of course are not a contributor to "button bloat" because the dedication of this hotbar to that purpose is of my own choice.
In the specific case of AST, I have all my card-related actions on the ASh row so I can see their cooldowns but I don't press those buttons. The cards are all macroed to two buttons on the neutral row, but with the changes to Minor Arcana and Divination I'll be able to eliminate one of those macros unless Play Minor Arcana is going to be a button separate from Draw Minor Arcana; I haven't looked closely enough at AST footage and Action Helps yet because I plan to heal Sage first.
Also also not pictured is by the limit break button I have a macro bound to Backspace which can swap between two bar sets, with the intent that this be used to switch between AoE mode and single target mode. In practice I haven't been using this on jobs I actually play often, but with the changes coming in EW, some jobs will be even better suited to splitting AoE and ST bars, so I'll probably use this more in EW, further reducing the hotbar demands of those jobs. If I ever wanted to switch to keyboard-only healing, I could also use this to swap between offensive and defensive bars.