The issue here is you are using arbitrary numbers to prove a point, whereas in reality, this isn't even close. Now, whilst I do not have numbers, upgrading your gear is going to be closer to ~1% damage increase, which is all you needed to theoretically bump your damage high enough to pull enmity.
To put some numbers to the potency loss for PLD to do their enmity combo, here are the numbers:
RoH = 640 total potency
RA = 760 total potency
This means, for every RoH combo you do, you reduce your damage by 26% for that one combo. Obviously, this isn't realistic, so, add in the good old GB + 2 combos from back in SB, and the nubmers change as follows (as a reference GB is 1090 total potency):
GB + 2*RA = 2610
GB + RA + RoH = 2390 (5% reduction)
GB + 2*RoH = 2370 (10% reduction)
So, increasing a DPS's damage by a few % can have lasting detrimental effects. This is before we then start taking other things into consideration, like the lack of recourses, the fact it took PLD 1 GCD to swap to tank stance and another to go back to DPS stance, which also both took MP in a time where PLD's MP was so finely tuned, you had to rely on the passive MP regen over a minute to ensure you had 10000 MP for Req. And then, to top it all off, being in tank stance cost you 20% of your damage and you pretty much had to be in tank stance if you needed to build up any reasonable amount of enmity, as your enmity combo in DPS stance did not build up much at all. It was a very similar situation on the other tanks, with Warrior being one of the better ones due to oGCD tank stance swapping and access to Unchained to mitigate the damage loss (though they still lost access to Fell Cleave).
However, irregardless of this all, it still felt bad for you to be actively punished because the DPS was playing well. It could have theoretically been a DPS gain for the party in some circumstances, however, it doesn't change the fact it felt bad to do and THIS is the core reasoning why the tank stances were bad, especially in SB.
Your aim was getting back to 10000 MP every minute (since HS cost 2000 MP then), in order to get that MP, you had to Riot Blade every time, so, with 3 GB and 4 total RA combos, that is 7 total Riot Blades per minute and even then, you had to rely on the natural MP regen on PLD in order to only just get back to 10000MP before Req came off of cooldown. This could be supplemented by Sheltron giving back some MP when hit, but by doing that you also 'wasted' a defensive cooldown. Things were tight back then.