I just had a weeird thought while I was writing a chapter, but...what if Starlight Glimmer was the magic bearer in each of those verses with the exception of Nightmare Moon? I mean, we see daylight, so in each we know that there was a set somewhere, its just that those particular bearers couldn't beat those respective foes. Now, what if Starlight was magic in each of those?

She was too selfish in the empire to know the meaning of sacrifice for the greater good.

Lacked a connection with Cadence to be able to stop Chrysalis

Gave up too easily with Discord

Couldn't handle Tirek because she took over and never allowed the group to gain their keys

And in Nightmare Moon, made it so Celestia couldn't find a student in time.

(I got nothing for Flim and Flam. Love the joke, but wonder if it was appropitate and the writer wanted to get to the next scene.)