I honestly don't see the problem that others are seeing when it comes to Rainbow in this episode. I thought she was great, and her conflict actually made me feel sympathy for her.
It was a genuinely hard decision and a conflict applicable to real life, and it was too much for her to bear so she tried to quit.
Doing something like that can be GOOD for a character and their development,
because despite being a cartoon, they should be allowed to make bad decisions and mistakes like a REAL person would.
What's important is how they realize they messed up, and how they correct it. Fluttershy gave her some touching sentiments, and then she came clean in front of everyone and gave another speech to spitfire. This was doing it WELL, in my opinion. VERY fitting for Dash.
Rainbow got extremely motivated in Games Ponies Play because she was thinking of the heartbreak she had as a filly when Cloudsdale didn't get the hosting rights.
She also got very excited at the prospect of training flag-carrier fillies for the games, drawing from the wonderful experience she had as one.
She thrives off competition, she IS a born winner. Her dream is to join the best flight team in Equestria. To make a name for herself.
Characters running past her = She says "Oh, are you two having a race? Can i play? 1-2-3-GO!"
Can't decide on a pet = She holds an epically elaborate contest.
Her heroes ask her to compete alongside them in a huge public sporting event? Hmm....decisions, decisions. OF COURSE i'd expect someone like her to take them up on their offer. It's the natural response.
Some people over-analyze this show and point out the illogical. THAT'S the problem. A cartoon is supposed to entertain and be viewed as a big picture, not be broken down so much over the tiny details that all the fun and life is sucked dry. We even find out that Fluttershy would've had NO PROBLEM with Rainbow joining them. She UNDERSTANDS Rainbow because they're such good friends. THAT'S why i didn't mind Rainbow's indecision, and THAT'S why i think the choice wasn't meant to be obvious. Twilight tried to TELL US THIS by NOT forcing a stance on Rainbow, telling her to decide for herself. This indicates that both sides held merit.
"Not choosing to choose... isn't a decision" is one of the best moralistic lines this show has ever done.
That's all that needed to be said, and it truly felt like Twilight was channeling Celestia here.
She's becoming the foil and guidance for the characters, which is GREAT because it reflects her changed role and gives her something to do.
Her story arc is OVER now that her studies are complete, and the show is now more about the entire cast than it's ever been before (emphasized by two characters in this ep),
so we should take what we can get when it comes to deciding what to do with her. And personally, i think what we're getting is very nice. Some of you are saying that Twilight was too soft on Rainbow? I say that we have completely different understandings on who/what was at fault here, and who was really being a jerk. (hint: they actually got told off)