Christopher Michael
Troubadour
This is what I've always thought -- that reinforcing character traits can be done in revision. But won't that make you run into problems? For instance, if I can use Fifth's example with the man kicking the dog, #1's personality directly affects what she does.
So let's say that the man kicking the dog is the villain. If only #1 sees this happen, she'll go after the guy and confront him, which could lead to him being revealed as the villain or whatever. But if only #2 sees this happen, she won't do anything, and the confrontation won't have happened. This can change a large part of your story.
You're not wrong. However, this is not a minor characteristic of a character, but an intergral part of how they interact with the scene. Whether they come across "flat" has nothing to do with this. How your character reacts to something like this is something that should always be at the front of your mind while writing.