Stances are remnants of an old system of DPS agro management. I believe the stances were a complete oversight by the Dev team and not recognizing the the lack of desire of coming out of one stance as a DPS. Reminds me of the ninja stances from YEARS ago that got the axe in HW I think?
The stances for mnk have and in of themselves always been trivial. Like you I can probably remember only ONE time I used fists of earth and it was when our tank died in Dazmel Darkhold on the 2nd boss due to standing in AOE. I flipped over to fists of earth and due to high DPS I held agro easily. Back then we had featherfoot and this accompanied with bloodbath, second wind, haymaker, fists of earth mnk could truly hold it's own in a tank situation until the tank was rezzed or until the mob was dead.
Where I think monk went off the rails was from 1.0 into 2.0. Monk has always been considered a tank from 1.0 and a lot of that carried over into 2.0 with bloodbath, second wind, haymaker, fists of earth and in 1.0 you also got Taunt (now provoke), but is no longer available on monk currently from 2.0 onwards.
Monk is a failed experiment of a former tank in 1.0 being turned into DPS while still holding onto a LOT of skills focused on tanking into 2.0. I totally believe monk could have been a tank in 2.0 if it weren't for the positional's. Which I feel were tacked on to put monk in the DPS category to make it compelling to play. If positional's weren't there and monk kept everything from 2.0, it would be a tank. My god your role + cross class allowed: Foresight (defense), Skull sunder (enmity generation), fient (slow enemies), keen flurry (parry chance), Bloodbath (HP regen), Not to mention featherfoot (evade chance), Haymaker (counter on hit ability that slowed), Fist's of Earth (damage reduciton), Mantra (increased healing), one ilm punch (removed buffs).
This ALL makes me believe and this held true in FFXI for monk. But Monk was going to be the 3rd tank in 2.0. There I said it.
Paladin - mitigation tank
Warrior - Life steal tank
Monk - Evasion/dodge tank (and without positional's this would have been AMAZING)
I truly believe monk with it's high DEX and Evade chance monk was a "dodge tank". Fist of Earth in 2.0 gave 10% damage reduction...Fist of Fire only gave 5% damage increase.
Haymaker was actually REALLY strong with 180 potency and a slow effect when a monk evaded an attack. Pretty reminiscent of Shield Swipe with pacify on block for a paladin.
The key here is positionals, and the unessicary need for them at ALL in this game. FFXIV didn't understand what it was until heavensward. After the complete overhaul of 1.0 and 2.0, heavensward was the real start of battle mechanics imo. Everything before it was something to get them started with the game. Monk was just a by product of an old system that nobody liked, and monk has been confused as to how it fit in the DPS world ever since leading up to 5.4.