Lots of actors have played a role as challenging as Hamlet or Macbeth. But no one has played a role as challenging as Joan Smalls. Frankly, I never even knew there was a character named Joan Smalls. The only Joan Smalls I’ve ever heard of is a model. But who am I to question the genius writers at Yahoo! Style?
Of course, if the writer meant that Joan Smalls faced a challenging role, then that would require an apostrophe: a role as challenging as Joan Smalls‘.