But then you have to look at his muscles to, he's really strong which make the bike "lighter for him".
A lighter bike is easier to throw around, that's true. Many on this forum seems to be sort of against weight saving which I clearly can't see why. When I made my bike 1 kg lighter it made a huge difference to my riding, I could go way higher and longer, and got generally smoother and I'm a beginner. It takes less power to do the moves with a lighter bike, Don't trust me? Feel free to hang on 3 kg weight on you or the bike and ride!
So the conclusion is, yes it's worth to make it lighter if you can afford it.