When Shadowbringers came out I was really surprised Clemency didn't go to the chopping block or get changed into an oGCD with 90 sec cooldown or something. Would've solved this problem right quick. Same deal with Cure 1 and it still not getting a trait just upgrading it into Cure 2 and getting it off of peoples hotbars baiting them into thinking they're supposed to use that. Some of the most problematic skills we have; as you may probably guess you're not the first or the last person who thinks they're supposed to be using Clemency or thinking that using it over Holy Spirits and moonlighting as a healer is a playstyle choise. It really isn't. It's just really poor efficiency.

The thing is, even (good) healers don't want to use GCD heals unless they have to. None of the other tanks have a GCD heal and they all have similar mitigations and do just fine so it's just weird that PLD even has that, especially since a lot of people start tanking on PLD and obviously fall into that trap.

It has its uses. It can prevent a death with good reactions if someone is low before a raidwide and you're not sure if the healer can get them. It can prevent a wipe and keep a run going if the healer kicks the bucket. You can throw it on yourself every now and then if you really don't trust your healer for some reason but you should still aim to get your requiescat buff and do those DPS spells; mobs dying faster is mitigation in and of itself. It's just that you should never use it if things are going even halfway decently as doing so is just a pointless DPS loss when healers have OGCD heals.

If you enjoy GNB then that's good but if you liked PLD aside from having to be told that spamming heals is bad tanking then I find it weird that you're so hung up on that issue. You take Clemency out of the picture and both of them are essentially doing the same thing: cycling their mitigations and maximizing DPS.