A lot of problems are also due to old systems. Ask any plumber. The plastic pipes are smooth inside. Old pipes weren’t only rough, they degrade. Cast iron sloughs off into itself. There was a kind of pipe that was used that was basically tar paper; it broke down and clogged itself (like cast iron).
A new building with new toilets should work very well. Replacing your toilet may not help if your pipes from the 60s are basically nonexistent.
