The problem here is you are defining "complexity" in a very traditional way and how you see it. Over many centuries music gradually got more complex in a pretty consistant way, and even then, if complexity is the criteria, then Bach is the greatest composers of all time, end of story, however we know that is very debatable. For Bernstein, it is Beethoven the greatest composer of all time. But I don't want to elaborate on this, however, one thing does bother me, is the necessity and insistance to make a point of this. I use to think this way, but I've changed over the years, it is possible that Gerswhin is more complex than the Beatles, however, the fact that the musical language of pop, jazz, blues, rock, is entirely unrelated to traditional music, in other words, you cannot make fair comparasons. In jazz, for example Bill Evans has different types of genius traits that are really unmeasuable. You mentioned the Beatles, they are a result of a lot of musical genres, including rock n roll and blues which was the language of their time, and their amazing abilities to come up with a unique sound and chord changes quite unique to rock n roll, and I refuse to measure the complexity of genres that I cannot personally have a full understanding of or play myself as with the same ease as classical music, and for me to evaluate superficially and make comparisons is quite pretentious. Many of the musical qualities are passed on by ear. I don't know what is your background other than classical composers, but there is another world out there.
The point is, maybe it is more complex, maybe it isn't, maybe it's the same, I don't know and frankly don't care. When I'm in my car these days I'm listening to Beach Boys, I'm in awe in front of what they did, some other days I'll enjoy Bach, and both equally, just in different ways.
It's fine if you want to give your opinion about this, however, people who tend to want to make a point and insist on the complexity aspect with compaisons between Beethoven and X with their traditional criteria, need to get off their high horse.
Sorry I feear you argue against something inexsitent. I am not defining complexity, nor did I insist on anything nor am i riding on anything. Just to mention that many great composers in nearly all kind of musical genres have develloped in all times overwhelming examples of musical complexity and there for there is no reason to rule out complexity as one possible qualities of music seem to be in fact not that far away from your statement.
The more inapprorpiate sounds it to me if you end up your argumentation with personal allusions like "people who ....iniists" ( "who exactly insists here on exactly what????) or "need to get off their high horse" who exactly is here on what ever kind of "high horse" ??? So please read next time a bit more carefully before becomming personal. Stay calm and focussed on the real subject. Oh my musical background is as colourful as the century is in which I grew up. 😃
It is not that difficlt to know, if you would have take the minute or two to see what I have done in the last years. (there is enough online) So it is kind of funny being reminded at "another world out there." by someone who has already difficulties to read the postings exactly in front his eyes and do not know nearly anything about the one who he actually is talking to.
So I do agree and will likewise remind you that there is obviously "another world out there." which you might understand with a bit more interest and curiosity much more, than with argueing based of missing understanding and prejudice.