CEMFI is worth trying. But can you handle the potential disappointment when you re-apply 2 years from now?
How confident are you to become one of the top students among your CEMFI cohort? How confident are you to get strong LoRs? What if you cannot even get into OSU 2 years from now (no offense to all CEMFI students)? And when you cannot get the same tier admission you are having this year, will you look back and wonder "what if..."?
Not saying that you should definitely choose your phd offer over CEMFI, what I meant (and I believe what most others meant) is that I think when being attracted by the excellent placement record of CEMFI these years, you should also consider the potential risks you are taking.