Beethoven had trouble adding 2 and 2. Seriously.
, I was wondering whether intelligence is an underlying characteristic of most successful performing pianists.... or are things such as creativity or artisticness more important?
What? He was a pretty shrewd businessman, so I have trouble with that notion. Where did you read that?
Perhaps we should distinguish between intellectual ability and intellectual interest.There are people who have a need for intellectual stimulation. They go to the library a lot, they wonder how things work, they try to figure stuff out, they want to know more. Learning academics isn't a chore for them, they enjoy it. They tend to become research scientists, some types of engineers, etc. They like to debate and discuss and nitpick. They do not tend to become piano players. That doesn't mean a piano player might not be just as intelligent, but by and large he/she is interested in art, creativity, etc. He does not find long solitary hours in the practice room as boring as the first type might.
Some form of intelligence is necessary to do anything really well.