Researchers find pre-Columbian agave plants persisting in Arizona landscapes

I assume you're talking about Leach's papers. Leach chose a particularly small family of Agaves for his work that also stores less energy per kg, and chose very conservative numbers beyond that. His results, given all that, were unsurprisingly that Agave is just barely worth growing on a caloric basis.

Better estimates are that typical agricultural varieties produced twice as much heart "meat", at more than twice the caloric density he found. It's a much better crop in that light, but it's still not comparable to maize. Agave is also an amazing utility crop (the fibers are good for cloth and rope, the spines for needles, the heart for alcohol), a good border crop to keep animals out, and it's incredibly resilient to climatic conditions that would kill any other crop.

Agave was basically an agricultural insurance policy before global trade networks and financial systems existed. If you were worried that a heatwave or a drought might affect you, you could plant a ton of it on marginal land somewhere and leave it alone for years until you needed it.