Batman's villains are much smarter and more classic
the genius that is killer croc. or clayface. or two-face. or killer moth. and the list goes on. whereas 97% of spidey's villains have at least 1 phd.
Batman has Ra's al Ghul, Hugo Strange, Hush, Simon Hurt, Owlman, Prometheus, Bane and the Calculator if you want highly intelligent foes. Meanwhile, Spider-Man has Rhino, Tombstone, Mac Gargan, Sandman, Hammerhead, Big Wheel and a bunch of other folks who have never formed their own team or organization because Marvel is clearly afraid that such a measure will make Mensa obsolete.
Really, don't bother raising indefensible points. Particularly if you're going to describe Harvey Dent as dumb when the man was a highly accomplished district attorney.
What I meant when I wrote smarter and more classic I meant the people who made them created them in a smart way, not that the characters themselves have high IQ.