Sheltron is not as strong as SE thinks it is.

[Reynhart]

Because any good PLD worth their salt won't use clemency unless healer(s) are ded or it's prog.

Any good PLD worth their salt knows that if you're in need of an additionnal cooldown above Sheltron, it's better to use Clemency than to die.

I didn’t mention clemency because it’s closer to equilibrium, storm’s path, abyssal drain, souleater, Aurora and brutal shell.
While clemency is certainly stronger than those due to its spamability, it also costs GCDs and mp that could be spent on dps unlike the rest of the tank’s moves so is generally not used as often compared to the other tanks.

Like as I said above, as a tank, your priority is to survive. In you're in a situation where you dont need Clemency, the little difference between Sheltron and its counterpart is negligible. If not, you would survive when other tanks might not, especially DRK and GNB.