If it makes you feel better, "one third" is realistically a reduced precision approximation of something like 23/64 (from a genealogical perspective) or near 33% of certain markers on a genetic panel.

Well, I think it's a bit different. The Little Mermaid takes place in an unidentified kingdom on the surface (it seems vaguely Italian or Mediterranean, I guess?) and an underwater Atlantian kingdom, so race doesn't matter. The original Dr. Strange comics have all sorts of uncomfortable racial and religious tropes; it's about a white guy who finds magical order Tibetan monks, not only learns their magic, but becomes even better than them at it, and moves to New York with an Asian man-servant named Wong who serves him tea. Changing up the races and backstory on that one isn't just acceptable, it's advisable.

Exactly Ariel is basically fish,

I have mixed feelings about Liam Neeson in that role. His performance is great, and given that they got rid of the whole, "immortal genius from the Islamic Golden Age," backstory, I guess the character's race is less important. It feels very strange that an Irish guy is somehow the leader of a group of Asian ninjas, though.

The Sam Jackson/Nick Fury story is pretty hilarious. When Marvel created the Ultimate Universe in the comics, they changed a lot of characters' backstories. One of those changes was making Nick Fury black, and one of their artists started drawing him looking a lot like Sam Jackson. Jackson talked to his agents, and Marvel was basically like, "Well, instead of suing us, would Mr. Jackson like to play the character in any future projects?"