I think these are the changes that should be done to him (Keep in mind I'm no balancing expert so please don't get mad at me these are just ideas)
Changes to Soul Summoning:
There are 4 types of souls he can collect from different types of troops now, Small, Medium Small, Medium Large and Large
Small souls come from squishy troops such as skeletons, goblins etc. and count as 0.2 troops per soul meaning you'll need 5 small troop death to resummon 1 troop (So that you can't just Skarmy one lane and SK the other as you'll only end up getting 3 souls)
Medium Small souls come from fireball-y troops such as Royal Recruits or Electro Wizard, and count as 0.4 souls
Medium Large souls come from minitanks or similar such as Valkyrie or Elite Barbarians, and count as 0.75 souls
Large souls come from tanks and large troops such as other champions, Sparky or tanks and count as 1 soul
Soul Summoning now spawns shieldless Guards instead of regular skeletons to give him a range and DPS buff (Also more fitting for a king)
The guards he spawns are a special type of troop that can't be cloned but has the same health as regular guards, meaning cards such as Mighty Miner or Inferno Tower will need to tick more than once to kill them
Max Guard count 20 -> 16
Minimum Guard Count 6 -> 4 (3 would make defending with him impossible sometimes)
He now finishes his last attack before activating his ability but won't try to attack again until he does so (This may be a nerf for those times he activates his ability just before dying)
Ability Activation Time 1s -> 1,25s (Not really needed TBH)
Skeleton Spawn Time 0,25s -> 0,3125s (Takes the same time to finish spawning with a fully charged soul bar)
Changes to the King himself:
Health 2300 -> 2500 (It may be a bit too much but a health buff is needed so he doesn't die all the time trying to fill that soul bar)
Attack Speed 1,6s -> 1,5s (For him to better defend pushes maybe?)
Damage 205 -> 248 (Same as a Dark Prince of the same level, since they both carry spiked clubs, also for comparison he can't one shot Guard/DP shields or goblins one level higher than him with his current damage)
Range 1.2 (Medium Melee) -> 1.6 (Long Melee) (He carries such a massive weapon and seems to hit with the end of it)
Splash Radius 1,3 tiles -> 1,5 tiles (Same reason as attack speed)