Nearly all of the parts are designed around a small set of common interfaces. The main change is that have moderately increased the number of interfaces vs. a few decades ago and there are more small decorative parts (and thus higher overall part counts) in most large current sets.
Designing models that are comparable to the first-party models is a more difficult challenge for kids than it used to be, but there is also a much larger pool of extremely skilled builders than there used to be (both adults and children). But there’s nothing stopping anyone from using the current pieces in older-style projects, and the older pieces couldn’t be used in quite as large a variety of models as the current ones.
Designing models that are comparable to the first-party models is a more difficult challenge for kids than it used to be, but there is also a much larger pool of extremely skilled builders than there used to be (both adults and children). But there’s nothing stopping anyone from using the current pieces in older-style projects, and the older pieces couldn’t be used in quite as large a variety of models as the current ones.