When is Rainbow Dash going to learn her lesson?

[BalanceBrony 259]

Just because it's true doesn't mean it's not boasting

 

Part of me wants to selfishly say yes because her arrogance is the one and only thing I dislike about her, and without it, she would be perfect to me. However, without having a flaw, I suppose it would make her character unable to grow and develop, which would make her character less interesting I suppose. I still think she could just tone down the arrogance a little bit though ;p

Also, as @@Anadu Kune,  mentioned, she has toned it down a bit. She said "It was nothing." Previously she wouldn't have added that bit of humility to her statement, and the statement would have just been "Yeah, I'm awesome." She's still arrogant, but less so than before, showing some development. But like Twilight's funny little freakout in the premiere, the writers still need to make it clear that RD is not perfect, which mean she's pretty much as developed as she'll ever be in terms of canon territory.

[Empress Pinkamena 41]

Ponies aren't perfect.  She's still going to boast from time to time.  However, in Mare-Do-Well, she was constantly going on about how wonderful she was and how everypony needed to worship her, to the point where her arrogance started endangering others.   There's a difference.