When there were majorities in Mexico, when Congress was faithful to the president, we didn't enjoy the benefit of grand visionary reforms. Today, the states that have majority governments that are noted for their innovative drive. Gifting an addictive majority to the president is a shortcut and could be a trap.Leo Zuckerman disagreed yesterday, pointing out that no one wants to give the president anything, but merely make a majority a more likely proposition than it is today, i.e. the US.
I think Herzog-Silva's point about the shortcut is worth remembering; Mexico's problems don't all come from a lack of majority. Although I'd add that a shortcut isn't necessarily a bad thing; why suffer from 40 years when you can suffer for just four? (The one about state governments is not; governing is completely different at the state level in Mexico.) But I'd say the bigger concern is with regard to reconstructing a strong presidential system that in the past facilitated authoritarianism. Such worries have a long historical precedent to back them up, but at some point Mexico needs to stop being governed by its fears* of a return to authoritarianism. If the first priority of your democracy is preventing the circumstances by which any leader can conceivably make his leadership permanent, then you necessarily shortchange many other worthy goals. Such a priority is understandable in a newly non-authoritarian country, but it can't be a permanent feature of government. Any mature democracy needs a certain measure of trust and acceptance; you accept the legitimacy of the opposing party's government, because you trust that they'll give you the chance to do the same when the time comes. But part of accepting the legitimacy of the winning party is giving it a reasonable chance to implement its agenda. Not a timid facsimile of said agenda, mind you, but the policies upon which it campaigned. In Mexico, all of this is absent, from the trust and acceptance (see López Obrador) to the implementation of an agenda to the campaigning on policies. The results have been manifest for the past decade; the system spins its wheels eternally, but it actually moves forward only in the rarest of fits and starts.
*I would have referred to such fears as "atavistic", but lately I can't use that word without feeling like a boorish showoff.