"Mediocrity" is such an ill-defined concept. As you advance out of being mediocre, the pool of people you compare yourself to gets smaller, and you still end up feeling mediocre. When you get to Elon Musk levels, I would assume you switch from comparing yourself to those you know and instead compare yourself to historical figures (e.g. Henry Ford) and perhaps still feel mediocre.
Then add in the Dunning-Kruger effect (the real one, not the popular misinterpretation of "you're so dumb that you think you're smart") and judging what exactly mediocre means becomes even more difficult.
But in the end, sure you can convince yourself that the negative feeling of not achieving as much as you might have been able to isn't worth losing sleep over, and you might end up 'happier'. You can also try to leverage the feeling to stop yourself from wasting those 50+ hours rewatching Game of Thrones and instead putting that time into becoming more like someone who you perceive as being less mediocre than yourself.
Then add in the Dunning-Kruger effect (the real one, not the popular misinterpretation of "you're so dumb that you think you're smart") and judging what exactly mediocre means becomes even more difficult.
But in the end, sure you can convince yourself that the negative feeling of not achieving as much as you might have been able to isn't worth losing sleep over, and you might end up 'happier'. You can also try to leverage the feeling to stop yourself from wasting those 50+ hours rewatching Game of Thrones and instead putting that time into becoming more like someone who you perceive as being less mediocre than yourself.