I can attest to that. Love me some El Pollo Loco. I also used to be nuts about Alcapulco, and too many hole-in-the-walls to count. I've been in Texas nearly seven years now, and still haven't found anything to replace the Mexican restaurants I loved in L.A.
I have had Tex Mex, as well as Arizona style, but I think SoCal authentic places have better flavors and ingredients.
As to the difference, between “Americanized” and authentic Mexican...you don’t get much more authentic than eating in East LA.
I’ve been to Mexico, but prefer their food up here in the states better.