Good stuff. But, as you said, Arryn raised his banners and sent Robert and Ned to raise armies. Without his leadership it wouldn't have happened. Lord Hoster was obviously suggesting restraint initially, because he didn't want Brandon and his party going to KL to demand Rhaegar. All that said, I don't think it was a foregone conclusion that Robert would be king when Aerys was ultimately deposed. I think he would have been fine had it been Jon Arryn, even without an heir. He could have named Robert his heir for whatever it was worth. It was a pick when all was said and done. Robert was not opposed to being king and he did have Targ blood, so he was heir to the throne that way- although not truly with Viserys and Daenarys alive. Ned seemed opposed to being king. His father's Southron ambitions appeared to have soured him on engagement. After the Greyjoy rebellion he completely withdrew from the other Kingdoms and remained in the North. He didn't even have marriage pacts arranged for his heir who was of marrying age or his bastard who was as well.