Cowell is a great businessman but I hate what he has done to the music business. People used to spend years in the pubs and clubs, cutting their teeth, learning their craft and if they were good enough and had some good luck they would get signed and quite possibly have a long career ahead of them.
Now they go on these shows (from stage school in most cases), and if they do well they will get a short episode on his conveyor belt, before they fall off the end and are replaced by someone else. There are one or two exceptions but they are few and far between.
I honestly dont think the Beatles, Stones etc, wouldnt stand much chance of breaking into the business these days. 
I can't understand why you would say that mate? because they were the thing at the time... My daughters both know who each of the Mega Acts you mentioned how many of todays acts will be as popular in 40years.... could Take That be there equivalent today??
These were artists, and very talented artists they were too.Almost all of the famous people these days arent artists by any definition that I can think off.
Comparing Take That to the Beatles is imo like comparing Richard Clayderman to Mozart.
I cant see them being thought of as the biggest most influential band in history 40 years after they break up (again) tbh.

I am convinced that popular music reached its pinnacle in the late 60,s and it has been in a steady decline ever since.
For me, most of the people who are worth listening to today are people who are survivors from that era. They may be getting a bit old and crusty, but I dont see many people coming up to replace them. Its unlikely that anyone will, as not only the business but the world has changed so much in the intervening period.