Isn't starting a brand new product line on an already full market a very different task from managing an existing product with a lot of legacy users and a famou

Isn't starting a brand new product line on an already full market a very different task from managing an existing product with a lot of legacy users and a famous name? For an analogy: Tim Cook is a great manager for Apple, but I don't believe he would be a great founder of something similarly big on the contemporary smartphone market.