I'm no one to say, but as I recall things did not happen that way...
AeroMexico does not rely on Mexicana to operate. That is just not a valid statement. Each carrier has to support its own weight and pay off its own bills. Each carrier has been extremely profitable up until last year.
AeroMexico's strategy has been different. They are conservative when it comes to expansion and they are not trying to conquer the world for the sake of having an impressive route map. They already tried that once and it didn't get them anywhere!
My opinion is that they are following the close example of their partner Delta Airlines. Delta is equally known to be very American conservative (the attitude of the Southeast) They expand slowly but surely. The don't like take steps without first really making sure that they're doing the correct thing. If you notice, AM acts exactly the same way.
Then, you take a look at the U.S. route map. They tend to concentrate their activity towards Delta's big hubs. Also, AeroMexico tends to be more worried about having more frequencies to their destinations rather than operating a few flights per week to many more destinations like Mexicana.
Mexicana on the other hand likes to do things differently. They have an impressive international route system but many of these destinations don't have a daily flight. Some examples I can think of include: Buenos Aires, Montreal, Sacramento, Oakland, Denver, San Salvador etc. etc. While they are rapidly expanding internationally, their domestic route system is much smaller than that of AeroMexico.
Now history wise, I can tell you that things are not the way they were told to you. From what I understand, Mexicana had nothing to do with the 767/757 purchase. The 767/757s were originally ordered by AeroMexico to supplement their DC-10s, back in early 1990/91. This was before AeroMexico purchased Mexicana, which was on the brink of shutting down due to extreme losses. The original batch of 767s, were ex-Lan Chile aircraft, while the 757s were factory new from Boeing's plant.
Then, AeroMexico bought Mexicana and soon after that AeroPeru (See where that went). Some of the 757s were transferred over to AeroPeru. While, I did learn there was some sort of conflict in 1996/97 when Mexicana wanted to operate 757s, but AeroMexico had some opposition. So when Mexicana got its way, they literaly stuck their tonge out to AM by stating on their new 757s, "No que no" and "Vamos por mas." "I told you so" and "we're going for more."
During the 1995 Tequila crisis, AeroMexico and all of its subsidiaries which included: Mexicana, Aerocaribe, Aerolitoral, and AeroPeru were taken over by the government in order from preventing them from total collapse. Thus, Cintra was born. AeroMexico has done that, been there... It learned its lesson.
As far as I know, AeroMar was never a part of Cintra. AeroMar only code shares with Cintra's carriers.
Pan Am - The World's Most Experienced Airline.