Bevendre

I shan’t apologize for my statements, but allow me to explain.

Celestia is worst Princess:
Though bearing the visage of a kind and understanding ruler who would rather interact with her subjects than stand above them, Celestia is an incredibly flawed character who more often than not refuses to acknowledge her own flaws.  The beauty of the characters of the show is that they aren’t perfect, but they acknowledge this and grow, Celestia has not done this.
In regards to Nightmare Moon and Sombra Celestia failed, to an extent.  With her sister, instead of trying to find a median and prevent Luna’s descent Celestia left the problem untreated as far as canon shows.  Though Celestia solved the ‘problem’ of Nightmare Moon she did so by banishing the problem rather than fixing the issue itself while reformation was a possibility before the fact and after through the use of the Elements. (This is shown through the later reformation of Luna through the Elements being used for the first time by a group who had virtually no knowledge of them prior, whereas Celestia had used the Elements at least in part against Discord, and therefore would be more aware of their capabilities.  
With Sombra the problem was solved, again by casting it aside that it may be dealt with later.  This was likely not the intent, nor fault of Celestia, what followed however was.  In the case of both Nightmare Moon and Sombra, rather than acknowledging that she had failed, that she had not done everything that she could, Celestia hid information, or worked towards its hiding.  This may be seen with the realization in the pilot that Luna/Nightmare Moon is related to Celestia producing shock in the Mane 6, most notably Twilight who is especially close to Celestia.
Celestia is not an active Princess, and if anything is less so than any other in canon.  What’s more, she hides and ignores her problems instead of acting to fix them or asking for help from others that she may fix them.  Instead she waits for the problem to worsen, and sends others to fix it.

Discord is worst villain:  
Discord is not a villain.  He is an antagonist, yes, but he’s not a villain per se.  Rather than acting against any character he sowed chaos and disorder in a land that was once his own.  Discord is a trickster, not a malevolent entity.

Gamer Luna is a valid representation:

Just because handhelds and most videogames are not canon to the show does not mean that they would not be intriguing to Luna if they were.  In “Luna Eclipsed” Luna exhibited a willingness to learn more of the modernized world she had been put in, and an excitement to learn more of the more trivial distractions of her subjects.  Her excitement and joy at playing carnival games displays an interest in the modern and a desire to not only catch up on what she had missed, but to be more relatable to her and to find distraction and joy outside of her duties.
Videogames are a wide reaching, relatable medium through which many find this exact thing, and though they may not exist in so many ways in the SHOW, the concept of Gamer Luna does and is supported by show canon.  The premise is supported, the games are added on to make it more relatable to people.

If my opinion is not to your liking, then so be it.  If you have a problem with it, then provide a counterargument.  Unfollowing someone because they exhibit an opinion at odds with your own does not help anyone, discussing the opinions does.