What TB misunderstands about kingship/monarchy

Too often I see the simplistic argument from them that Rhaenyra is the rightful successor because "the king said so and the king's word is law", but not only is this overly simplistic, it's actually backwards.

Rather, being able to exert your will onto your subjects is what makes one a king, and when they cease to obey you, your rule is called into question. In my view it is more correct to say that "I am king because people do what I say", as opposed to "people should do what I say because I am the king".

If everyone else in Westeros woke up and decided that whoever on the Iron Throne is no longer fit to be king, and therefore disregarded, deposed, and/or executed them, then they would no longer be king as a matter of fact.

I think half the realm disregarding Jaehaerys' chosen successor is enough to call his kingship into question, or at least the absoluteness of it. There were always implicit limits to the power of the Targaryen monarchy, like how they were forced to give up polygamy by the Faith. In this case primogeniture is a firmly-established component of Andal customary law. And I do call it "law", not simply "tradition", because it is evidently something that many are willing to use force to uphold.