Eh. I actually rather disliked daybreaker-- it just WASN'T tia.
her personality and motivations didn't synch up with celestia at all. I can forgive this for being from starlight's thoughts, not celestia herself, but its still "wrong". Daybreaker being all laughter and energy just felt a bit off.
Celestia has never shown a desire for power in the past, so having daybreaker be all about "THINK OF HOW POWERFUL YOU COULD BE" just isn't doing it. Having daybreaker focus more on anger at Luna for not understanding how much responsibility she had for 1000 years running the country, or the sacrifices she makes, or feeling that she is more trouble than she's worth would work, but not the random "UNLIMITED POWAH" thing that daybreaker had going on.
Daybreaker being just angry and bitter and being "You're a massive pain in my ass and I want you GONE", with her telling celestia "Just think about how much BETTER things will be when we get rid of her! You know you want it!" as the main crux of her argument would have felt better IMO.
Celestia just has more elegance to her character than that, I figure a nightmare celestia would be less crazy and more vain.