The Big One – “Obviously that would be both lashan hora and sheker (which all lashan hora by definition is)”
simply said – your definition is not correct
from “Chofetz Chaim – A Lesson A Day” Aleph Tishrei “…Loshon Hara refers even to true statements… untrue statements are termed hotzaas shem ra, slander”
from Zelig Plishkin “Guard Your Tongue” page 29 True derogatory statements are Loshon hora and false is called motzi shaim ra
you can’t believe it, but your not believing it does not make it false.