Certain classes are weaker than others though
Yes and no. Obv Sword Saint is overloaded, base Alchemist is strictly worse than Grenadier if you know how to cast Delay Poison, and Eldritch Archer was unfortunately completely mailed in.
Other than that Owlcat did an extraordinary job giving almost every class a way to excel if you work at it.
NJClaw's (and InEffect's) tier system is about how good a class is solo, but that's just a different game. P:K is at it's heart about group synergies.
The way you talk about the tier system makes me think you have never seen a single PnP Pathfinder session.
The tier system I posted has nothing to do with Kingmaker, it's about PnP classes' versatility. And it's not "mine", I wish I was JaronK, I would get laid so much more.
That tier system doesn't say that a certain class is "stronger" than another in combat, that's not the point. It doesn't care about which class gives which bonus.
And, while I obviously respect and love Owlcat for the amazing game they gave us, they had nothing to do with the Pathfinder-related content that's in the game. Every class has ways to excel because Paizo designed them, not Owlcat.