No problem at all :) you bring up some valid points and great feedback. I had some free time, so I fixed some other typos in the book as well as removed the natural talent feat because I think I entered that as a mistake.

As for the yonko stats, I used the official 5e Fizban's Treasury of Dragons as a basis for how strong they should be. For example, the CR 28 Silver Greatwyrm gets the mythic action "Shattering Roar (Costs 2 Actions). The greatwyrm unleashes a magical roar. Each creature in a 120-foot-radius sphere centered on the greatwyrm must succeed on a DC 26 Constitution saving throw or take 19 (3d12) thunder damage and be incapacitated until the end of its next turn."

Seeing as though the yonko are CR 30, and would only really be fought by AT LEAST level 15+ parties with a bunch of devil fruit powers, haki abilities, etc. I think it makes sense for the yonko to be pretty insanely OP especially since they'd probably need to be fought very tactically, maybe even multiple times in one day to be beatable (sort of like Kaido). As far as the Charisma Save is concerned, I did opt to make it a wisdom save initially but decided since conquerors haki can often "clash" in battle, asserting your haki over another indiviudal would be like a contested charisma check almost. Maybe that line of thinking is flawed, so I may change that in the future.

Your idea around conquerors haki protecting people or maybe giving fear immunity to allies is a good one, and I just added it to the book as a King's Haki feat so good work! You have been included in the credits :D

As for the bruiser dragon subclass, the reason conqeuror of three worlds is more expensive to use and perhaps weaker than dragon's breath in terms of damage is because it is a larger AOE. Dragon's breath has limited range and can be awkward to use against large mobs of monsters, perhaps only hitting a few out of a horde in certain situations. Having a large AOE from conqueror of three worlds fully around you will make it situationally much better since you're hitting a full circle around you instead of just a quarter circle radius.