Yeah, a big part of the flavor difference between Mexican Coke and American Coke really comes down to the extra sodium in the Mexican Coke variety.
You can get the US formula coke with cane sugar during Passover in markets with a high Jewish population. Taste it, it'll be practically the same as HFCS US Coke and not like Mexican Coke. Because, it has the same amount of salt as the US variety.
The bigger difference, imo, is that Coke just tastes better out of a glass bottle. Orifice size and shape makes a big difference in taste and mouthfeel.
I definitely agree that the container can make a big difference on how we can perceive beverages, and I don't doubt it's a part of the experience fans of Mexican coke enjoy even if they don't realize that's playing a role.