Actually, Yes it is that severe. Any flashes on any dark ride is distracting and annoying.
The "No Flash Photography" rule is there for a reason, and it isnt just to be mean and not let people take pictures.
As a gay man, I can assure you that the dresses are very pretty, and in my opinion do not look like a nightgown. Go for it!
I'm 40, but I'd love if I could dress up all spiffy in nice prince regalia. (a Disney prince, not the purple guy :laughing:)