Except when fighting single powerful creatures for the defense of Risur the Monarchs powers are not overwhelming.
The monarch of the land ability has been useful outside of combat to change geography but a few 4th level spell (Wall of Stone/Stoneshape) or a small army of minions could do the samething
+5 untyped bonus vs charm, fear and poison, nice enough but poison with the DC tp bother 18th level characters are rare, most of my pc's could drink pints of deadly poison and only have a 1 in 20 chance of noticing, Charm and fear are more common but if expected protection from evil, mindblank and Protection from spells should be up so really a niche benefit , don't think the monarch has used it yet
I forget how bad the fast healing 10 is , it only kicks in if you are dropped below 0 hp , fast healing does not work if you are dead, so an attacker has to reduce you below 0 but above about -18-24 hp. With the massive damage common in pathfinder combat at this level death is more common.
Ability to give anyone else a reroll against charm/fear or poison nice buff for everyone else but has yet to come up.
The mechanics of the monarchs powers are not that great (except against titans), so mechanically there is not a lot of reason to give people buffs to match it.
Socially it is a big thing but all of the pc's should be Dukes following the attempt on Aodhan and are likely to form the royal council so decisions for the nation are likely to be collective and in any case pc's are likely to concentrate on smaller scale events like saving cities from heroic threats.
One pc may well be a member of the unseen court with better mechanical boosts (at will invisibility and immunity to mindcontrol), for others there is the possibility of trying to usurp a Fey Titan , with no defined abilities but the prospect of many. Then there is the Godmind urn if anyone is crazy enough to play with it. And for technologists/gunslingers there is the madness of Steam suits and tinker/ob toys for crazy good guns.
I did consider letting the monarch delegate her titan fighting powers but I was glad she had them as her powers applied to some of the the pc;s would have seen Granny Allswell dead in a round, the monarchs powers are at their deadliest given to a mellee combatant.
The various artefacts are not that great, the Swords of Ssramma waste a lot of their bonus on cool but not very useful powers , The Arsenal of Dhbisu is nice but changing shape does not fit with many combatants feat trees and it lacks the truly great enchantments but its such a cool weapon I buffed it for the pc who got it.
and sadly '
The title of Green Knight is bestowed to the king’s chief bodyguard.
Among the position’s perks is an inability to die when the sun isn’t up.
This ability requires a close connection to the Dreaming, however, and
at the end of this adventure the green knight loses all of her powers'
Otherwise that would be great and very abusable although without some other trick you would still stop fighting at negative hp and so it is mot much better than on tap resurection via high level cleric.
And no item beats the Absurdist web as a perk
Overall my group suspected from an early point that one of them would end up as Monarch and they all knew which character it would be as three of the 4 original characters had a charisma of 8, the replacement could have been monarch but joined the unseen court instead. I had no jealosuy about it depsite the same player ending up as Queen of Talingarde in the last PF campaign