Okay, this right here is the problem with your idea, you've completely misunderstood the entire point of GLA/PLD, you are
not a 'holy knight' at all and never will be, you're just a spectacle fighter from the Colleseum who has equipped a fancy crystal that allows you to quickly master some elite sword and shield skills from the Sultansworn, the royal guard of the Ul'dahn sultanate (and they're not even holy knights either - their scheming, underhanded conspiracies throughout the PLD Job quests showed that), when the GLA Guild no longer had anything more to teach you. In this game PLDs are not 'holy knights' that wield white magic like in other FF games, you're closer to a generic knight than a holy one (in fact, the actual name for the Job in the JP version literally is 'Knight' not PLD).
Also Goring Blade was originally (in the 1.0 release of the game), specifically a
GLA ability - it was one of the abilities dropped when the battle system was redesigned and Jobs added, only to be brought back in
Heavensward as a PLD ability. And we'll probably continue to see more old 1.0 abilities gradually return (I'm hoping for Phalanx, Red Lotus and War Drum myself

).
Also with GLA/PLD's abilities being simplistic, that is the
point. GLA/PLD is deliberately meant to be the 'beginner's tank' that is easy and simple to use with a basic ability set that anyone can pick up and master. That's not to say it's 'baby's first tank' though: it's more than capable of being a force on the battlefield, it all depends on the
skill of the player. You could reduce the battle system to little more than "Press X to hit the enemy and O to defend" and you'll still get people who would muck it up. At the other end of the spectrum, they still want it to be accessable to new players so hence the more simple mechanics of the class/Job.
As the old saying goes:
"a poor craftsman always blames his tools.." 