1. The dragons would be much more vulnerable if everyone else was inside the castle because they would have have to hover (which was bad) or keep away. Then the Night King could just sit back and let the dead win in a battle of attrition as they mentioned in previous episode.
2. Also already explained several reasons but even beyond that its pretty silly to expect a horse riding culture of honor to fight on the walls. (
In the Behind the Scenes its already explained that the Dothraki just attack because thats what they know and Daeny can't stand to see them die which messes up the plan - again could have been explained better.
3. Plot armor. I already said some scenes should have been shot different. Jon's ice blast was obviously one of them. Yes the blast that took down the Wall could be stopped by a stupid rock pile. That shot was indeed awful, agreed on that.
4. Its not Drogon and Daenerys I would be worried but Rhaegal and inexperienced dragon riding Jon Snowgaryen. I wouldn't trust Jon to evade an ice javelin.
5.
The Night King brings the Night. Literally. There is no "attack during the day" option mate