I do agree that its importance is overblown, especially by old school sports people. However, I do think clubhouse leadership can help. Pretending it doesn't matter at all is a flaw of analytics IMO. Players are human after all.
For context, they weren't saying that they were only signing him as a leader, but they were saying that it was a big part of why they'd identified him as a target compared to other all star level infielders (as they and many others rated him at the time).