Unless immediately replacing a DoT or badly overcapping a buff's duration has suddenly become a contextually viable strategy, that is exactly how each tank works. They just spend a lot more buttons on the same non-decisions and their ability to hit anything else during GCDs are determined by durations rather than durations and contexts.
DRK has only one offensive GCD ST choice between gauge spenders; it just happens to spend 3 buttons (Hard Slash -> Syphon Strike -> Souleater) on it instead of 1 (gauge), meaning it gets two fewer actual actions. Much the same can be said for AoE (Unleash -> Stalwart Soul in place of Holy). Naturally (i.e., without Delirium or Blood Weapon), DRK generate a gauge spender every ~21.25 seconds by which to use a "ST Action #2," admittedly a bit more often than a healer. Choice count: equal. Button cost: Double or greater. And the kit size and depth are not compensated for that cost.
PLD: DoT (3 step; takes 3 buttons). Filler (6 step; takes 3 buttons). Ranged filler (4-5 steps; 1-2 buttons). Ranged DoT (3-4 steps; 1-2 buttons). You maintain your DoT and otherwise follow your filler sequence. The only added points of control are the timing of Requiescat (the action, not the phase) and Atonement count once per minute if you'd otherwise risk desync.
GNB: Better combo on a 30s CD (6-step; takes 2 buttons, down from 4 in ShB). Filler combo (3-step; takes 3 buttons). Far more frequent bankable spenders, though.
WAR: Better combo on a 30s two-charge CD, effectively (3-step; takes 3 buttons). Filler combo (3-step; takes 1 further button). Twice-bankable spender.
Apart from perhaps GNB, most tank gameplay (yes, easily 80+%) is just hitting filler combos in their various forms. Heck, if playing with mods, that filler play, and the vast majority of GCDs used, would be literally one button.
That's not to say such is satisfying, far from it, but it does indicate that perhaps the best way to invigorate tank and healer gameplay aren't merely to give them more button hoops through which to perform the same non-decisions but instead give them actual decisions pertinent to their roles.