"I believe that Columbus found maps - or at least legends - that came from the Vikings, who reportedly heard the stories from the Irish."
I've read that Columbus deserves great credit for combining politics, business and technology, to reach a goal.
A Modern Manager, of sorts. History proves his discovery made the world different, which none of the other alledged discoveries did.
True enough the Vikings preceeded him, but little came of it, save perhaps maps.
Other explorers contributed knowledge of ocean currents, which went into his calculations for an attempted new route.
He put it all together, complete with national sponsorship and funding.