The word mediocre is subjective and this just devolves into an ontological or semantic argument surrounding the meaning of mediocre. What’s mediocre to you may very well not be to lots and lots of other people. Or—if you prefer—in the form of an aphorism: ‘One man’s trash is another man’s treasure.’
Mediocre iOS developer who doesn't self promote versus mediocre iOS developer who does.
Since 90% of everyone is mediocre, a culture that encourages self promotion just fills the world with crap.