The PRI is sometimes described as "centrist", basically by default, because the PAN and the PRD are much more aggressive about staking out a specific ideological terrain. However, the label is really not ideal. More than centrist, the PRI is amorphous and opportunistic. And depending on the issue, it is outright conservative. As this poll from Excélsior shows, the PRI is basically indistinguishable or even to the right of the PAN on a number of social issues.
Also, Peña Nieto polled at 50 percent of the projected vote according to Excélsior's latest survey, compared to 29 for Vázquez Mota and 20 for AMLO.
Finally, Peña Nieto said that it was simplistic to propose legalization of drugs. Surely, he's right: even if you favor it, "legalization" alone is a slogan that leaves far more unanswered than it solves. If only Peña Nieto would flesh out his thought process a bit, under the pressure of adversarial questioning from people with different points of view. Like, say, in a debate.