There are no bad keys signatures for piano. There are only bad pianists
Technically, there are no bad pianists either. There are pianists that are struggling to play piano. There are pianists who have a lack of taste in their music. There are pianists who struggle playing fast notes. But there are no bad pianists. "Bad" is a big word. "Bad" kinda means that they don't deserve to be pianists, much less than being a famous, talented, and gifted one. "Bad" means that they shouldn't be pianists. I just wanted you, stevensk, to know that calling someone "bad" is a very big insult.
Anyways, back to the question. I don't know why it matters is some keys are piano friendly and some aren't. To me, all of them are the same. I like some keys better because IMO, they make a more beautiful melody, and for some keys, you can easily make a ragemode song for example. Take, for instance, c minor. IMO, you can make a sad yet beautiful melody, and you could also make a angry and raging piece. I agree that Beethoven thinks c minor is the stormiest and most violent key.