Haha, necro'ing this because I never saw the question.
It has been more than a decade since I read the last book of that series, but I remember that Luke had been very absent the entire series (like you said).
He hadn't really fought many Vong, but then he is at the battle of Courscant and he has no trouble fucking them all up unlike every other Jedi in the series. He is so in tune with the Force that the Vong aren't invisible to him, they are simply negative spaces of life instead of positive like every other living thing. He rips them up and really doesn't have any trouble with their leaders either. I just remember being very satisfied that when Luke decided to enter the battle l it wasn't even close anymore.