who told you that oxford generally give people aab-abb offers for maths? That's rubbish- none of the oxford mathsmos from my school (8) or any of the TSR mathsmos got AAB offers for oxford; poor dom had to get AAAAB.
Good for you if you can do the oxford entrance paper without any problems- i assume you're exhaggerating, but even so, the example papers on the website are all a lot easier than the real ones generally are, having seen about 10 years worth, collected by my school. I expect they put up easier examples so as not to deter good applicants who may lack confidence.
I'm not debating that cambridge is the better place for maths, and it does indeed have more stringent entry requirements, however, you're wrong to assume that getting into oxford is easy, or that it's easier to get into than warwick; many people are rejected by oxford but accepted by warwick. Warwick only require STEP/AEA if you aren't doing further maths, btw.
As for cambridge being 3000X the city oxford is- have you actually been there yet????