Majora's Visage
Smash Journeyman
It's an interesting question. You bring up all the points to suggest that Skull Kid still had some control up until maybe when he cursed Link or even with Summoning the Moon.Post 2000!!!!!
Skull Kid definitely has some bandwagon effect behind him, trust me this place was pretty inactive before the direct. Not that I mind though, it's Great having more people around to talk about the character.
Question for you, when do you think Majora's Mask took full control of Skull Kid? Was it instant? Gradual? Something else? Something new? When Skull Kid put on the mask, did it just become a wicked manifestation of Skull Kids personality? Did it act Skull Kids dark buried desires? Skull Kid was the one who attacked Happy Mask, so he's clearly not completely innocent. And Tatl and Tael didn't exactly notice much change, they still chose to help him ambush Link. And Skull Kid showed his child trickster like personality here too, playfully using the Ocarina and trying to hide it from Link when he wakes up.
A lot of questions and very mysterious
There is a really cool theory on the Mask itself on YouTube here https://youtu.be/guXHxiCAvSU
It's kind of long, but I think it's really cool. Honestly I would love if we got a Zelda prequel where we see who Majora actually was