Holy seal does in a way bring something new to knights especially going against our arch enemy class - the mage. Before this knight need to plow their way thru enemy troops before can land a hit on oppoenent mage, while the mage pound us w/ barrage of aoe atk. And if we r more unlucky, the mage single atk also directly hit us instead of the troop.
Archers also have atk that can randomly hit any target, sometime bypassing the troops to hit straight to main char. But theres no such option for knight.
Yes we can start w/ ultimate slasher n pray that it will targeted the main char but w/ holy seal it make it a confirm target. Else we need to hack n slash thru enemy troops 1st and hopefully when we reach the main, we still have enough hp to kill them lol. Yes we have shield but it wont last long specially in high lvl pvp.
I think holy seal also does make ppl rethink their strategies - fast lvl to get new skill point is good but also risking getting stun in pvp; too much xp spent on talent making lvling slow n missing important skill... theres always a pros n cons to it.
Imo, it does give some advantage in a way but not totally OP.
Just my 1 n 1/2 cents