Post was better than the episode but I digress.
Given she was in the water with every other character, yes it was important. Why capture her and not try to kill/capture anyone of military value?
Line of sight also works both ways, and it seems Euron had no trouble seeing them. Given what we've seen on the dragons throughout the series, they would have known they were there far before Dany. Like when Jaime was charging her after Dany ambushed them leaving Highgarden.
No, I don't think Dany was the difference. I think they just wanted to kill Rhaegal for dramatic effect and didn't put much thought into how. Kind of coincides with #2. Dany was flying Drogon straight at Euron and he couldn't hit him, after going 3 for 3 on a side moving target much further away. Was pretty stupid.
Like I said, hopefully this writing isn't a sign of things to come in the next 2 episodes. The overall quality of the show suggests it won't be, lets hope so.