That's true only if everything goes well for them and poorly for us and we have no chances to recover from then on. In canon two of those four dragon riders die before the succession crisis even starts. While we definitely shouldn't count on everything going exactly to canon - Daemon has no reason to assassinate Laenor here if he was responsible in canon, nothing has happened that would avert Laena's death in childbirth. And divergences can cut two ways - if Viserys lives a bit longer, Rhaenys might well die or become too old to fly before any succession crisis kicks off.
If things seem like they're spiraling out of control, I've got nothing against course correcting or preemptive action, and certainly once it's a real problem rather than a potential one Rhaenyra shouldn't act out of character in allowing it to fester. But I don't want to nip it in the bud before that point. Also, we picked the warrior princess background, we should expect to solve a decent number of our problems with violence.
Rhaenyra would be aligning ourselves with his rival who has conflicting interests to his. And also I expect having illegitimate kids would rapidly tank his approval, since he'd view it as Rhaenyra being a foolish girl.
His approval of defiant and headstrong princess is probably going to be hard to keep up, and I'd expect the best we can expect is fluctuating neutral to mildly positive.
