Devotion to the Targaryen house is admirable, but the truth is that Dany is a big "if" in the big picture.
The kingdoms got time, but she may not have that luxury.
Far as we know, she can't reproduce, which is crucial to maintaining a royal family.
The inbreeding Targaryens are known for can contribute to her not birthing an heir. Getting knocked up by her nephew Jon is a possibility that makes things even riskier. Also, those dragons haven't reproduced yet either.
Then there's her pride, something the last episode challenged with Jons true identity and Sansa not budging on what she wants for the North.
All 5 of those WW, maybe more, have to miss with their ice lances and that undead dragon has to be defeated too.
As it stands, even if Dany got the throne, the question is how long can she hold it. There's still the possibility of her (or maybe Jon) succumbing to madness like many other Targarenys before them. Thing is, even if Jon went crazy, Sansa and Arya have the balls to put their brother down while still upholding the Stark house. Dany's army is a bunch of deserters, hired muscled, and dragons that do whatever they want.
Y'all Targarens are high risk in the end game.
Danny got time, but not enough to procrastinate.