Haha. I can kind of see why. But the ship sailed a long time ago when it comes to arguing against this usage - it's not incorrect. The Oxford English Dictionary has it as "Of or pertaining to, or having the characteristics of William Shakespeare or his dramatic and poetical productions."

Language is an ever-evolving, often messy thing. "Shakespearean" has been in use since the 1800s, to refer to Shakespeare's own works. And, really, the number of examples you give in your piece kind of proves the fact that "Shakespearean" is entirely acceptable in this form. Thanks!

Thanks for writing!