Just a few corrections/thoughts on the original post:
The .38 Super is not legal in Mexico. The most powerful (in terms of kinetic energy) handgun calibers legally allowed are .38 special for revolvers and .380 for semi-autos.
You can read the text of the law in Spanish or use google translate:
http://www.diputados.gob.mx/LeyesBiblio/pdf/102.pdf
You are allowed 1 handgun for self-defense inside your home only (long guns cannot be used for self-defense, only hunting and target shooting). Hollowpoints are illegal for self-defense. All guns must be bought in person at the 1 legal gun store run by the army in Mexico City. So if you are poor and live 100 miles from the capital, are you going to buy a gun legally? And they wonder why they have an illegal gun problem (apart from the thousands of Mexican soldiers who have deserted in the past few years with their full auto weapons).
As far as the 9x18 Mak, I don't know why the Soviets came up with that round but I suspect it was not that they were looking for something more "powerful," but rather the opposite. Clearly, the 7.62 Tokarev was already "powerful" enough in terms of being high pressure and having armor piercing capability. I think they wanted something softer and easier to shoot from a pistol. What did they need a pistol for? Only as a badge of office for military officers and a basic weapon for police in a nation where most people were unarmed and complacent. Handguns in Russia (and many other countries) were/are not thought of as tools of self-defense, let alone combat (you use rifles, tanks and bombs for combat) but of authority, so a .380 equivalent round is more than adequate in their equations.