> It's shown in 180 countries worldwide and very popular internationally (Including Russia)
If you pick 10 random people in Russia and ask them about this show, all 10 will either not have heard of it or react with disdain. I have no idea where you get the notion that it's popular in Russia.
> It's easy to say we aren't popular because we are smarter than everyone else
I was popular in Russia. Then I had difficulty fitting in at the Australian school until I learned to act like an idiot and not reveal my 'nerdy' (a word that doesn't even have an equivalent in Russian) hobbies and interests outside of select circles. The same hobbies and interests that were perfectly average in Russia - electronics, astronomy, chess, that kind of thing. After that I fit in again. It's pretty hard to interpret this as some sort of social issues like you claim. I think you lack perspective on this. This is also the same culture that teaches teenage girls to act dumb in order to appear more attractive, which is pretty well studied at this point and will hopefully die now that it's in the public eye.
> It's sad to me that there are children out there that can't actually be kids for awhile
As one of the kids who would match your label, I think it's sad that children here are artificially held back from their natural maturation in order for the parents to selfishly extend the baby phase for their own enjoyment. Nor does this coddling have anything to do with stability. Plenty of stable countries across Europe where kids are allowed to grow at their natural pace, including several first-hand accounts in the comments section here. This is also why you'll find significantly lower age limits for things like consumption of alcohol, drugs, sexual activity in those same countries.
Coming back to the OP topic, soviet textbooks are 'hardcore' because the pupils are 2-4 years more mentally mature than their western counterparts due to cultural and education system differences. It's as simple as that.