Picasso changed how the world viewed art and he was a great artist. His paintings are very unique and inspire many young artist to believe in themselves to create great art. There are many artists who are recognized but not remembered hundreds of years later. The fact that we are still talking about Picasso says that he was beyond great in his art work.
Picasso really was a masterful artist. His pieces do represent the apex of modern art. His paintings are so expressive and soulful, while being completely original and innovative. It is beautiful how jarring to the senses some of his works are. Picasso will go down in history as one of the greatest artists of the modern period.
If Picasso is the apex then why even create new art when it will never improve. In the context of how many artists exist and will exist one man is not going to be the apex. Besides a cubist can't be the apex of art, a dadaist or surrealist could though.
I'm not knocking Picasso, but aesthetic beauty is relative to the viewer of the art piece. There are no parameters we can use to "measure" art's value. We can define it using such terms as realistic, impressionist, surreal, etc. but how the art is appreciated is up to the individual.
Picasso is not the apex of art, mainly because there is no apex. The greatness of art is relative and trends in art are often cyclical. So many people may think of Picasso as the highest achievement in art, while others may think it looks like childish garbage. He is considered a great artist, but there will be many more great artists after his time.