It's not a good thing. I love fictional arrogant/conceited characters.
Seriously, though, there's a difference between growing as a character while maintaining confidence and getting your ego annihilated. It seems like whenever Rainbow Dash needs to be taught a lesson, they have to mentally assault her until her ego is non-existent. They had the entire town act like it was the zombie apocalypse just to show her pranking needs to be done differently.
Like I said, though, I enjoyed Newbie Dash and 28 Pranks Later. My favorite episode is actually The Mysterious Mare Do Well. I just enjoy Rainbow Dash more with flaws than being humbled into obscurity.