This statement is misleading because the broad appeal of both Shakespeare and Mozart today is the culmination of centuries of attempts to understand (and misunderstand) them. Calculus can be taught to high schoolers nowadays, but how many scientists in Newton's days could understand the Principia in its entirety?
Not to mention that Shakespeare and Mozart were both able to produce works of the highest sophistication that leaves most of their contemporaries (and many today) baffled. Harold Bloom wrote that the sophisticated word play in Love's Labour's Lost was not surpassed until Joyce, and Mozart's contemporaries complained endlessly about the complex textures in his opera finales. When Mozart wrote piano trios for the public, his publisher cancelled the series after two pieces because they were judged far too difficult for the masses, and when Mozart intended to write some easy piano sonatas at the end of his life, the first (the only one he completed) turned out to be the most difficult he ever wrote.
Invoking the popularity of Shakespeare or Mozart as analogues to Mr Beast reveals a fundamental misunderstanding of the longevity of both Shakespeare or Mozart, and leaves unmentioned the extensive body of difficult works on which their reputation rests today.