You have 3 classes at 50, none of which are in the same side of the Holy Trinity. If you had some first-hand experience with all 9 jobs, you'd know exactly how different they play and how different you have to think about what your current and next actions are in a changing fight situation.

TANK

WAR mindset: big hit's coming up, how do I get an Inner Beast ready? Shit, didn't get to 5 stacks in time, gotta pop a buff

vs.

PLD mindset: bit hit's coming up, I'll just press 1 button and call it a day.

(alternatively)

WAR mindset: Overpower, overpower, overpower, aoe tanking all day erryday

vs.

PLD mindset: Flash, flash, flash, shit lost hate to Flare whatdoidohelp

HEALING

WHM mindset: aoe heals, top everyone up with regen, might throw some stone and aero out but gotta watch my mana

vs.

SCH mindset: tra-la-la dps for days, mana for days, don't even need to leave cleric stance to lustrate, let the WHM worry about stomps

DAMAGE

MNK mindset: boss is about to jump, how do I keep GL3 up through the jump? idgaf if the boss turns, my combos will still hit

DRG mindset: Heavy Thrust/Impulse Drive missed because the boss turned to do fireball/landslide/fffffffffff

BLM mindset: when's the best time to pop manawall/ward so I can keep casting without moving? Nice, got a Firestarter proc, I can reposition again finally

SMN mindset: dots for days. Had to cancel a Ruin cast? I ain't even mad

BRD mindset: Wait is this game supposed to be hard?