I think if you do a protect the king tournament you should augment the stats of the "king" to make them tankier than their teammates.
It's possible to edit the stats of different troops serverside, meaning you could change the ironflesh value to give them more HP (each ironflesh is +2 HP):
The base value is 3, which can be raised up to 10, +7 being 14 extra HP. I don't know if you can exceed the 10 limit, that would have to be tested if you wanted to.
Additionally, all troops are using the "def_attrib_multiplayer", which as you can see below is equivalent to 15 strength, 15 agility, 15 intelligence and 15 charisma.
Each point of strength is +1 HP, but it also has an effect on how much damage you deal. Agility makes weapon handling better and makes you slightly faster.
Imo, in a format where the death of one person means their team loses the round, that individual should be tankier than the rest of their team. The "king" is supposed to play safe, that's the whole idea of the format, but in my experience if there's a 7v7 protect the king tournament it usually becomes a 6v6 with one person from each side essentially playing spectator inside the arena. Making them a little stronger would incentivise them to play the game more, creating more potential for them to be caught out, rather than just s-keying the whole time so they don't die and lose their team the round.