If you really think about it, Celestia stepping down from power and handing over control of Equestria to someone that is unqualified for the job; has no actual training when it comes to matters of government, or even has as much political sway compared to Celestia is the same story for both settings.

Fallout: Equestria had it with Princess Luna; where she had no idea how the government actually operated due to being on the Moon for 1000 years and had no clue to how much times had changed. Meanwhile; the only work that Twilight actually knows how to do is being a Librarian in Ponyville plus the Principal of a School she had created; only to immediately be pushed into the deep end as the end-all-be-all ruler of Equestria.

I believe a Mormon said it best: "Only Caesar can lead the Legion."