First of all I would like to start by saying my argument does not apply to SELF guards. I get why those are limited.
With every other defensive Ability that targets Someone else you can use it unlimited times. The Kings guards are just a regular Support Ability that gives someone night Immunity. This isn’t stronger than a heal or a sacrifice and is often weaker than both. The only thing that a guard protects agenced that a heal does not is a trap and even there the reaper has gather darkness. Beyond that there are meny things that heal protects against that guard does not: Poison/Bleed, Bear, Sacrifice (the attacker not the Knight) ect…
So it definitely isn’t OP to have guards infinite use. So why don’t they? Infact even if it’s OP for a regular king that could be the thing that seperates the starting king from the others.
Note: The King would still only be able to self guard 3 or 4 times. Otherwise it would be OP.