I really didn't find this funny at all either, I was expecting some kind of big joke all the way up to the end, and then left disappointed.
The only good thing about this video is that it points out that Sakurai patches won't always do what we want it to and can end up making the game worse considering his design philosophies.
There's something to be said for adapting instead of complaining, but there's also a point where something is jank and we need to acknowledge that. It's like saying "Meta Knight isn't broken, you just need to adapt". Diddy wasn't Meta Knight levels of broken, but he was clearly stronger than the rest of the cast and he needed to be nerfed.
I think it's less that Diddy was super jank and more that the bulk of the other characters were and still are trash, if not even more so now with how it nerfed R.O.B and Link almost as much as it did Diddy.
The power gap between say, Sheik/Rosalina and Charizard/Samus/Mii Sword/ect. is still much, much larger than the one between pre-patch Diddy to Sheik/Rosalina.
What I feel the patch should have actually done besides nerf Diddy is buff all the low tier characters, but now instead it'll just be Rosalina/Sheik/whatever other high tiers just melting the rest of the cast instead of Diddy. who's still miles ahead of over half the cast.