Well, they were saying the exact same thing in the 60s - that rock music was less complex and a watering down of Tin Pan Alley-based pop.
I think that a basic important point here is that complexity in music is hard to measure. It depends on the measuring rod that is being used. If we are looking only at harmonic complexity, for example, then it looks like popular music has become increasingly less complex since the mid-20th century. If we measure by rhythmic complexity, we will get a different result.
And, or course, we could also argue about the relationship between complexity and quality in music.