Should you combine Mexico City, Oaxaca and Yucatán in one trip?
You can combine them, but only with enough time and a willingness to move. In a shorter trip, Mexico City plus Oaxaca or Yucatán plus Riviera Maya often feels better than making every region fight for two nights.
Answer
Mexico City, Oaxaca and Yucatán make sense as a first-timer dream because they show three different Mexicos: capital-city intensity, food-and-craft inland culture, and ruins, cenotes and Caribbean edges. The catch is the connective tissue. Every jump takes time, planning and energy, especially when you factor in airport transfers, heat and local transport at the other end. If the trip has around two weeks, this route can work with discipline. If it is closer to a week or ten days, one region will feel short-changed. The better question is not whether the route is possible, but which part you want to remember properly.