Regarding the scorpions, again, I think that this point is overblown. Dany lost her first 2 dragons to carelessness, as she (and them) weren't even thinking that anything can hurt them. When Rhaegar (the second one?) was killed, he wasn't expecting anything like that — got the first arrow, panicked and remained an "easy" target. Plus we have to assume that Euron is an übermensch that mastered the art of shooting perfectly, but that can be believed in a fantasy story.
The only truly shocking part was that they didn't spot his fleet in the first place.
Now in this series Dany
1. Attacks with the sun at her back, making it harder to spot her
2. Minimises the surface of her dragon by flying straight at them — Rhaegar made himself a bigger target as they attacked him from his side
Plus not everyone is as overpowered as Euron — the guards on the walls had very limited training, if any. And they are in panic, obviously, don't discount that.