Yeah I agree challenging middle class family values was important feature of 90s shows. That's why I liked Fresh Prince of Bel Air over Family Matters, it didn't try to fit blacks into the same mold as white middle class families, even as it showed a rich black family.
Also the stereotypical middle class shows like Step by Step, Full House, etc. were by that point cheesy and devoid of humor. Maybe they had a place in the 50s with Leave it to Beaver.