It shouldn't be a matter of their view v. your view. It should be a matter of the ticket rules, which very well may be exactly what AM is telling you. Or it may not be. If your pricing is segment by segment (which it probably is), it is not a stopover. You are probably on three one way trips ticketed on a single ticket. If your pricing is a MEX/LAX with a permitted (and included) stopover @GDL, it is a potentially different story. In any event, deleting a segment requires a reissue and repricing, as various fees and taxes need adjustment, and the two flight coupons need to be turned into one, allowing the nonstop flight. The only likely way to have an exception is for day of travel IROPS when the flights are under airport control and the agent may bypass the rules and deal with the accounting aftermath later.