He's right though. In the 70s and 80s they were all still the same character archetypes derived from the 60s TV show - goons, hideouts and deathtraps. Its only (relatively) recently that they've fleshed out unique takes on each of them. They struggled with the Riddler for decades. Same with the Penguin. And in Nolan's universe of realism the last thing he wants is another villain with a gimmick - like the Joker.
"Nobody cared who I was until I put on this top hat, monocle and cigarette holder..."