To the OP, yeah, Brooke was definitely very selfish for a large majority of S3 & 4 imo. This kinda falls into that category because really she shouldn't have to give "permission" to anyone to do anything, and that's kinda what it came across in 4.09.
But the purpose was exactly that though. Even though Brooke broke up with Lucas, he still kinda knew I think. At least knew that she still wanted him, but was mad at him, you know? It was almost like the break up was an "I'm going to push you away to see how much you care" thing. Like even though she was the one to break up with him, I think he knew she still cared a lot about the relationship type thing. But when put to the test... he didn't really put that much effort into it obviously, and didn't regret the breakup. & We soon see it's Peyton that his heart wants. And he knew this would hurt Brooke. I've always thought a big part of the reason he decided to be with Brooke again in the first place was to try and erase the things and mistakes he made in S1. And so in this scene, he's going back to Peyton - where it all started. It's what he truly wants and where his heart is, but there was some guilt there because of the past and just EVERYTHING. This scene was needed. It lifted LP's guilt (something that I think held them both back from a lot of things), and showed that Brooke would be okay - which was good for her character.
Despite popular opinion, I think Lucas is a really good guy with a big heart. So when the championship came and he was finally at a point where he could realize and admit it was Peyton that he wanted, there was still Brooke. And both, Lucas and Peyton, needed this. They needed and wanted to know that she would be okay because they both loved her! It was all a part of this process and it was like coming full circle in a way - where Lucas and Peyton could finally just be completely content and with each other after all this time. (: