He is right, Murray is best player on grass courts in 2012-2015 period, Novak is the more consistent one so he is always No.1 favorit for Wimbledon, but not better player on grass courts i would give Andy higher chances at best of 3 matches at Queens/Halle over top 10 than Novak - who plays only Wimby best of 5 last few years - so he can proove his consistency there while best of 3 at Queens/Halle - would be much tougher for him.
With Roger it´s more difficult he is No.3 favorit for Wimbledon, because he can get upset more easily by in-form players, because his defense and baseline consistency is not as good as Andy/Novak.
So Novak and Roger are only real competition for Andy, but if we say he is best on grass it´s o.k. i think. 2014 - was pretty bad for obvious reaasons, but when he has normal seasons, his game suits on grass, has serve, volleys, return and results there - at both Wimby and Queens over the years