Columbus is an interesting figure. He wasn't really a bad navigator, he just made a wrong assumption about how large the word was. He thought it was smaller and that he'd be able to sail around it easily. In that way, yes, he was lucky because, if there were no Americas, he would have ran out of supplies before he reached Asia. He managed to get a pretty good latitude though, so I wouldn't call him a bad navigator. This post from a while back goes into the navigation bits a way.

I can't comment too much on the ruthlessness but this post gives an nice nuanced view of him.

The Leif Ericsson praise confuses me a bit. Yes he was there first but he didn't launch waves of investment, settlers, and general colonialism into the New World that changed the course of history.

I hope this helps.