Jap is short for Japanese. It’s akin to using “Brit” or Mex or Aussie or Viet or Dane or Swede or Rus.....N****er is a bastardization of negro which just meant "black" originally. i.e. it's just an easier way to say "black". Does that make it any less racist? The connotations of a word are just as important as its meaning.
so we have a shortening vs. a bastardation. I don’t agree with the premise of your argument.