Okay. Here goes. My probably-going-to-piss-someone-off, honest opinion about this episode (and, by necessity, last episode, and to a lesser extent, Boast Busters).
First of all, let it be known that I love Rainbow Dash. For a good while when I first getting into the show, she was best Pony, and while she is now third that has nothing to do with not liking her so much as liking the other two (Applejack and Trixie) more. But I honestly don't think she is any different compared to Trixie when it comes to ego, and I would actually argue that Dash is
worse than Trixie when she is at her worst (as she was in the past two episodes. And, hell, Boast Busters for that matter).
I think it is a fallacy, a silly
silly fallacy, to try to use episodes of this show to teach morals about humility when one of the main characters acts like Rainbow Dash does nearly all of the time she is on screen. Hell, even when Rainbow is helping other ponies with their problems (for example, Call of the Cutie), she at least partially does it because she is
so awesome that she takes it as her duty to help others and talk herself up in the process. "One day you'll be nearly as awesome as me" and all that. And yet this is the third time this same basic plot structure has been used where Rainbow has been involved directly (Boast Busters and the last two episodes) and the ultimate moral had to do with humility, and this is the third time that Rainbow Dash has ignored the message outright and gone back to her normal antics immediately.
And I'm almost fine with that. I believe that character flaws are something that should be embraced rather than attempted to be written out. That's why I like this show, because they do that with the character development. The characters grow somewhat, where you can tell they are stronger because of character development, but not so much that you can't still enjoy the episodes where it actually happened. Twilight is less naive and introverted. Pinkie Pie is more trusting. Fluttershy can be relied on more. Applejack is less stubborn. Rarity is less of a prima donna.
I would be fine with the idea that Rainbow Dash is so egocentric that she can't learn the lessons being given to her, even though I don't think they should write her that way. But they
need to figure out what they want to do with Dash's character as the episodes go on besides "be closer friends with Applejack" (as great as that is
), because this "teach Dash humility but then immediately forget that they taught Dash humility" stuff is wearing thin. Do they simply not know how to write Rainbow when she's not hiring people to write autobiographies and generally just impersonating Duke Nukem?
And that brings me to my main problem with the episode, the one that has been bothering me so much: This was
The Episode that would correct my problems with the message given by Boast Busters.
Rainbow Dash, who acts like Trixie did the overwhelming majority of the time, was finally going to get her version of the message that was so mangled when they gave it to Trixie; and this time because it wouldn't be hypocritical like it was then, the message finally going to work. I didn't care that the path they could have taken towards teaching her her lesson could have been done much better than it was, particularly without straining the suspension of disbelief so much. I didn't care that Rainbow Dash was at times coming off as a caricature of herself (which was something that I didn't even think was possible). I didn't care that the episode was mostly strictly formula in the worst kind (read: boring) of way, even though making formulaic storylines entertaining to watch was a Season One specialty. I was even willing to overlook that 🤬 stupid Applejack joke that they made (Applejack Season Two character development = She names her hind legs). Because
THIS WAS IT. The moment of truth.
And then, they just didn't even bother. They gave Dash a moral that she shrugged off even quicker than she did in Boast Busters, then she went back to acting the way she usually did
before the episode was even over.
tl;dr:
Only Dash Good, Trixie Bad.
I want to argue that that's just how Dash is but I'd loose. You're right. 
