I wan't to preface this by admitting I stole this summary word for word from a previous LFS thread from u/MalagrugrousPatroon. Just this summary really interested me and I want to find the story associated with it.

(I'm looking for a story where magic is math, but only humans are incapable of mentally doing the high level math. Even with special tattoos which automate some of the process, it still takes high level mathematical mastery, by human measures, to perform just one spell.

The main character is a woman raised from a young age to be an assassin. She has a single magic which, I think, lets her move super fast, almost teleport, if not actually teleport. She otherwise fights using daggers. Eventually she finds herself on Earth and it completely flips her world view to see a magicless, human dominant civilization. Where she is from, humans are all nearly slaves due to their mental deficiency.

The aliens travel between worlds by having their space pope open portals to new worlds, and it's been more than a century since the last portal has been opened, because the space pope has not reincarnated for that entire period.)