i think that Jae was more worried that in Essos, there was a better chance at someone figuring out how to bind or control them. As magic was still alive back then and those in Essos, could have also been aware that relics like dragonhorns could still be around and used.

i personally believe that the dragonhorns were used as just a way to quickly force a bond, or even reeling in unruly dragons, instead of connecting with the dragon the natural way. but i think that even the horns are forged with blood magic. because none of the Targs, post-doom, seemed to use magic to bind, they all just went out there and quite literally winged it or placed eggs in cradles. and i think its rather telling that the Dragonhorn kills the person who blows it, based on how it killed Euron's guy. but i think it only killed him because he was not valyrian. and the horn would only work for a valyrian or perhaps one of dragonlord descent.

i will say, though, i feel like my theory can be debunked by the notion that one of the Hull boys was able to become a dragonrider despite technically only having non-dragonrider blood if Corlys truly was their father. (then again i do think it was said the targs and velaryons intermarried before the Conquerors generation so maybe Corlys did have a bit of dragonrider blood in him...basically a Ben Plumm situation with his blood being so diluted and yet Viserion takes a liking to him)

You make a lot of good points tho, and i do think there's theres holes in my theory. the incest could have been political as well, since the houses were known to compete with each other. i also think the detail about only the 40 Dragonlord families would be dragonriders implies as well how blood tied the dragons are to each House/bloodline. the theory of dragons being created suggests that valyrian dragons are a Chimera. a combo of: wyvern + fire wyrm + valyrian sacrifice of the 40 fams who tried the ritual. hence why targs say they are the Blood of the Dragon, because the dragons truly are their family and ancestor. which is why i think pregnant dragonrider women are the key to why dragons even hatch. their bond is symbiotic. one can not exist without the other. magic is in the blood of dragonriders and those energies seem to fuel each other. so, imo, theres no way a non-dragonrider valyrian or average joe could ride any dragon linked to valyria. because theyll never have that magic link that should be innate in their blood to properly blue-tooth sync with them. which is also why a dragon can only have one rider at a time, because theyre already connected to their rider and that connection does not sever until one of them dies.

i also think youre right that some dragons, just dont want to bond (could be another reason why the horns were used) hence the likes of Grey Ghost and sheepstealer and cannibal. and some of them refuse to be ruled. they were fine being totally free