Well there are several things about that chapter that makes me hate Rainbow, coincidentally is the same stuff I was complaining in the previous RD episode. I guess that boastfulness is a pretty big deal given the circumstances, but there is just no reason for RD to be like this.
Other bit that got me thinking is the canon nature of that event in Sonic Rainboom where RD just completely overlooks FS and only cares about winning, because the real outcome without the butterflies is just dead(crude but true), with that situation in mind I cant help but think that RD doesn't actually think about others, Mare do well is another testimonial of this behaviour, is just sickening that Selfishness prevails over common sense, and that really makes me think about the real canon RD which can be associated with all this.
These were the basis that are supposed to be redeem by her friends, and the supposed progression that RD takes to be a better pony(or whatever), but there is just no reason or redeeming values, just Scootaloo (and that was after the whole thing).
Heck, even Trixie cared about those two idiots when the Ursa minor attacked, and that is canon too. This fic deserves something which is the realization that RD is a complete a-hole, and that canon Trixie is better than canon RD regardless of backstory.