Congratulations on finding a use for cover, I truly commend you on that.
Hallowed ground I'm sure works great for buffalo too, as it is a physical attacking mob - once again I'm glad there's a use for it, though I am still underwhelmed by the 15 seconds. Some of these just seem too short a duration to make a difference - Hallowed Ground I would think you would use when things get rough; is that really enough time to recover? Perhaps the best use would be a situation where the WHM dies and you use it to get off raise.
As for Holy Succor, I suppose my problem is more that I usually go with a good WHM (career WHM from FFXI, played the job for years) so the only time I use it is when he tells me he's not going to cure me for some reason or another. I realize it is more useful in healing others, but most of the time I use it I see either me or my WHM's cure hitting for 0 because we both cured at the same time. I haven't run into enmity issues too much myself, but I think you're right in saying Holy Succor is useful for curing others
From the sounds of it, the abilities you get allow you to do great buffalo easier due to having enmity issues when it is reset.
As for the comment of survivability, however I disagree. Holy Succor is merely a more potent version of cure. While this is nice, it still requires a decent ammount of casting time, during which you could get hit and interrupted or killed. Personally, and I think others may agree, I find a combination of Second Wind -> Featherfoot -> Cure to work amazingly well for instantaneous and reliable damage mitigation and HP recovery. This also stalls for quite a bit, allowing for the WHM to have more time to get a cure of on you.
In short; sure, I agree, Holy Succor is great. The problem here is that Paladin is more MP reliant than Gladiator, and while gaining no noticeable defense, magic defense, block rate, or anything of the like, you trade abilities like Second Wind and Featherfoot and Deocy for highly situational (yes, you managed to find a situation for some of them) abilities such as Cover, Divine Veil, and Hallowed Ground.
The result is that a PLD has very little in terms of enmity generation or defense over GLA, while GLA has a great deal more useful abilities that allow it to stay alive longer. Because the two roles of a tank are to keep hate and not die, this makes GLA better.
Also, side-note: why is it that we have one hand devoted to holding up a shield, yet almost never actually use it?