It's all about how you look at basketball.
Korver is probably the best shooter in the league. Besides being a little weak on the glass, he is not a liability in any way. He averages 2:1 assist:turnover. He plays decent D. Most underrated is his ability to spread the floor. Countless guards can beat their man one on one. Help D is what stops them. You can't help if you have Korver or you will get punished. Guys that spread the floor don't get enough credit, and guys that penetrate get too much credit, IMO.
Westbrook is a much better talent, but he is a big liability. Korver never takes you out of games, and he'll give you the winning edge in a lot of games.
Westbrook will flat out take his team out of games at times. That's saying a lot considering how good his supporting cast is.