A leader might act like someone who makes some effort to lead teams, departments to achieve something either in opposition or government. A leader might learn how to negotiate, compromise and align in order to get things done. A leader might demonstrably show he can enthuse groups to achieve specific things.
A leader of a political party might not have spent thirty years snug and unbothered on the back benches making no attempt to engage or participate in the leadership of his party or indeed the country. It doesn't take leadership to carp and rebel from the backbenches.
It's pretty plain that he entered the leadership race for theoretical reasons, to have a debate and then shuffle off. Probably saw a book in it for him. I'm pretty sure he didn't see it like this and I'd suggest he is absolutely bricking it. If he wins he'll be looking for an excuse to quit "on principle" within two years.