Spanish is better than English, but it's nowhere near that regular. There are three different ways to pronounce "x", wild dialectal variations in "ll" and "c", etc.
In the last 40 years I've spent mostly in the USA I rarely have heard Uruguayan/Argentinian Spanish in person or in media, but was surprised to hear Messi and others in recent interviews use SH as in "puSH" for the Y/LL, this apparent has been a generational shift in that area, first in Argentina and then Uruguay. I'd sound old-fashioned if I were to go back to Montevideo these days.
"ll" in standard spanish is a strong english "y".
However, in spanish argentinian from the area of Buenos Aires (but not the argentinian Córdoba, which sounds more like colombian spanish) it is "sh", being that s something like a mix in-between of "j" and "s" + h as in "she" but the sound is a bit different.
Without being able to record some sound I cannot express it better but I am sure you can find something around. Javier Milei, the president, has such an accent.
In any case, her point wasn't to give a lecture on linguistics, but to impress upon the parents how complicated English really is to learn to read.
The first two are not productive now in normal Spanish words: they are only used in old spellings that have irregularly been retained, and in loanwords from indigenous languages. But they do exist.
Xenofobia is an s, yes, and excursión is "ks" In fsct, Méjico is the traditional way to write Mexico in Spanish grom Spain until it was accepted the other form a few years ago. I still write "Méjico" myself.
And anyway, as you point out, even in Spain the form México is accepted now.
After all, it is where they come from originally and have their own spelling (colour vs color, etc.)
An x in standard spanish has always been the two sounds I told you and that mexican deviation is specific to Mexico.
Yes, it is over 100 million speakers but I was still assuming the root language in its original place as the reference. Sorry if I did not express it correctly.
The "root language spoken in its original place" absolutely did pronounce X like modern J.