No? He doesn't even have a mental distortion, what is distorted is how he lives his life as per Rin's words, not some omniscient narrator. He just probably has an extreme case of survivor's guilt going by Nameless in Extra.
And yes 20 years is short if you have a leg up like Shirou, but it's not like it comes naturally to him like the Psychics who don't need to take a lot of time to learn how to fully use their powers.