You can't really beat up on Buenos Aires in particular for poor Mexican food: Mexican food sucks all around the world, with the lone exception of Mexico, and possibly California and Texas which have the great culinary fortune of having been Mexico until they were annexed in the slave wars.
The ingredients just aren't available elsewhere, where else are you going to find all the different chiles? Not to mention the different types of corn. And a basic bottle of Tequila costs 4600 pesos or so here or a bit over USD 20 at the blue rate, that's not bad by Euro / US price standards. Admittedly there isn't a lot of variety, but it doesn't really cost an arm and a leg either.
We're lucky we can get decent Peruvian food in Argentina, it's close enough for the essential ingredients to get here. It can be a lot poorer further away.
Your comment about the language is spot-on though