The idea itself is pretty good. I mean, shields are used for defence irl anyway, so it even makes more sense than the tiered ones, and it also brings out the knight’s potential as a tank.
It’s unique too. Shields generally give a pretty solid defence bonus, but only as a passive stat boost. However, just as you yourself admitted, it’s hella unbalanced.
I’d reduce the stat bonus to only 4 def, as it already provides a lot of protection with the ability, and -2 dex -2 spd, so it doesn’t cripple dps as much (the knight already has very little dex, with only the paladin having less).
This is just the beginning though, because what really makes this shield suck urgle tentacles is the OP effect.
The simplest way to fix that, would be to just reduce the length of the buff to something like 2 seconds (jugg has 4.5, with a 6 second cooldown), and maybe make it just increase ally defence by a constant like 15 or 20 instead (like tinctures/effusions), so it’d be a bit weaker by itself, but would stack with the actual armoured buff (This was done with the Cloak of Bloody Surprises, so it stacks with berserk).
It also protects the weaker players, like the random newbies scrambling around Lost Halls in T3 robes, which seems more like the knight covering others with the shield, whereas armoured would mainly just protect other meles.
The caster should imo just get armoured, like proposed in the original post, because that would encourage high def builds, and make def rings on knights a bit more viable, but if it gave a high enough constant boost, it could in turn encourage lower def builds, opening the way for things like offence-oriented brestplates and the like.
A maxed divine heals 90 mana in 2 seconds, so you couldn’t really permanently armour yourself (unless you had infinite potions), but you could stay armored for a pretty long time if you needed to.
A cooldown could be added too, but with multiple knights, you could stay permanently armoured anyway. Afaik those are only put on ablities that primarily affect the user.
A slightly more interesting twist, would be to make it work like a shuriken. In fact, I’m kind of boggled as to why there aren’t more hold-based ablities. It gives a lot more freedom and control than the standard way.
It would apply the armoured buff when held, consuming mana rapidly, and maybe adding a new debuff, that disables mana recovery, from all sources except wisdom, so it wouldn’t be too broken with a divine pet, but would still be useful without one. The projectiles would be shot when released.
It could also lower dexterity even further, or reduce attach a bit, so holding it would offer great protection at a price. Lowering movement speed would not be ideal though, because with low range and high defence, the knight is made to rush in quickly, deal some damage and retreat. Speed reduction would make it actually more dangerous to use, than a standard stunning shield, because when you hit the stun, you no longer need to retreat.
Lowering dps wouldn’t impact survivability at all, while still making releasing the ability close to the target worth the risk, despite the shield’s low damage.
Instead of lowering stats though, it could apply a weaker version of the darkness debuff. After all, shields block a large part of the field of vision, which is why police shields are made transparent nowadays.
As for the def bonus shared to allies, it could either be applied when held, alongside the armoured buff for the knight, or given for a set amount of time upon releasing.
On a side note: I think it looks way cooler with the rim and the cross painted gold, more akin to a beach of some sort.
It has a pretty nice contrast, and somewhat resembles the cobalt shield from terraria.
wall of text ftw
