Warwick is mediocre? Really? I struggle to believe that. Just because it's not Oxbridge does not mean its mediocre. Oxford and Cambridge are really good universities but they are not the only good universities out there.
You said, "No challenge, no other students to work with since most seem to be mediocre based on Warwick's low entry requirements." How can you base a university solely on its entry requirements? How do you know if students there have far exceeded the entry requirements? You haven't even been there, how do you know there's no challenge or no students to work with at a similar level to you? Do you honestly think that you are the only one at your level who has applied to Warwick? There may be plenty of students at "Olympiad level mathematics and competitive programming" that has applied to Warwick but you are drawing the conclusion that the university, the course, and its students are "mediocre" simply based on your shallow perception.
Not interested in knowing the details about how you got rejected but maybe it's because of your condescending and appalling attitude.