Mate, you've already gotten yourself ready to be lynched by titling your topic "The World's Best Pianist", which you definitely are not.
As far as improvising being necessary to be a musician (which I disagree with anyways), go into the world of jazz and you'll have your arse handed to you on a silver platter by people like Art Tatum.
Also, hate to be that guy, but Rafal Blechacz isn't playing 200 year old songs, not to my knowledge at least. I don't believe Chopin ever wrote any aside from the Polish folk songs, but even those don't have a vocal part, to my knowledge

That said, you don't have to create new music to be a musician.
Here's the definition of "musician" from Google-
"a person who plays a musical instrument, especially as a profession, or is musically talented.
" 'your father was a fine musician' "
If you want to make your own personal definition of musician include being able to write and improvise new music, then by all means do so, but don't act like that is suddenly the gold standard for musicians around the globe, many of whom are far better than you, my friend.
Cheers!