A person could have a well-founded belief in God without seeing him as Abraham did. What if someone in the early church had seen apostolic miracles and talked to an eyewitness of the resurrected Jesus? Would it still be a "leap of faith" for them to believe in God and his promises? I would say not. So I don't think verse 6 "requires some kind of leap of faith" in the sense you're using it.
I think such a person would still need faith, per verse 6, to put their justified belief into action in critical moments, e.g. at a moment when they're facing persecution for following Jesus.
Now, how much of a "leap of faith" is required given the evidence really available to believers then and now... that's the big question about which we presumably disagree.