Exactly this. We stayed at the Sheraton the last time and it isn't super convenient for transit, especially when we were going to places like Centro Banamex or Pujol, which aren't super convenient on the other end for transit either. (And we've always taken something from the airport as we don't want the hassle of multiple transfers with luggage in a crowded system.)

If we are near a Metrobus stop though and where we are going is close to another Metrobus stop, we will easily grab that, because of the dedicated bus lanes. e.g. walking from the Sheraton to MetroBus 1 for the Saturday Market. A bit of a walk on both ends, but we've done that a couple of times so know it and the bus is quick and easy for that. Actually, as I looked over our itin from the last time, I think it was more giving up on the Metro itself because of the heat and the crowds, but still using the buses half the time we were there. But very much agree with what Easbay1K said, depends where and when.