There were people making cohesive album statements before the Beatles. Frank Sinatra comes to mind, for starters. In the Wee Small Hours, for example, rates as at least as much of a concept album as anything the Beatles did.

Nonetheless, the Beatles brought a new type of consciousness to all this. In some odd way, the release of Sgt Pepper's initiated a kind of paradigm shift in popular music, different expectations about what music could sound like and still be popular. Before SP, popular music was fun stuff for the kids. Afterwards, it was ART. After this, it was not enough to say that a record had a good beat and you could dance to it. Not that that was always a good thing, but there it was.

Partly that might be giving the album a bit more credit than it deserves on the direct artistic merits. Why this and not Pet Sounds, say? Partly the Beatles were lucky here with being in the right place with the right album at the right time. They were making this big statement when the world was ready to hear it.

On the other hand, who would deserve such a historic recognition for so changing the popular consciousness more than the Beatles? I don't know how much of it was this particular album, but the Beatles overall certainly did more than anyone else in their generation to change the way the public overall thought about music, what it was even supposed to be about or try to accomplish.