The point of the laughter is that he's joyful and spreading joy
Psalm 2:2-4
2 The kings of the earth set themselves, and the rulers take counsel together, against the Lord, and against his anointed, saying,
3 Let us break their bands asunder, and cast away their cords from us.
4 He that sitteth in the heavens shall laugh: the Lord shall have them in derision.
He's so strong that he can win so easily that he is happy about it and he knows there is nothing to worry about and that's something amazing, to find joy in, which he and others do,
Joyboy was also really happy and had made whatever plans he and others in the void century or before it or after it did to help those in the future,
What reason is there to be sad in the situation Luffy's currently in, especially if he can just overcome anything and win against anybody, or if he will be able to soon?
That's also why the crew was very happy before Wano, they had trained for so long, Wano wasn't an arc that was there for struggle and loss, although a lot of struggle happened, it was the arc where all of their struggle and effort culminated to let them overcome the strongest,
And he did beat the world's strongest creature,