Being great at a sport doesn't mean you are necessary any good at player evaluation or team management.
Just look at any team Michael Jordan has run.
People fall into this trap, which is a nonsensical appeal to authority, all the time.
I'm not saying there aren't many players that can apply the firsthand knowledge they acquired from playing at a high level to make great player evaluations.
But all pro athletes were born with physical gifts that most mortals could only dream of. And a significant portion, to put it bluntly, do not have the intelligence to have ever made it into college if it weren't for those gifts.
I definetly don't assume an all time great isn't a great scout, but I also don't assume they are. I let them prove it and look at their track record.