Its not the fact that he is over top, its the fact that the supposedly Jerome character(future joker) is already acting like a full blown joker without the pale skin too early. In the comics pre joker was depicted as a comedian before the accident, but was not a full blown luantic until after it. I honestly think they got the Jerome character way too over the top for him not to be joker yet.
That makes a little more sense, but given the fact that they turned Jerome into a murderer in his first episode, you can't really do the slow burn with him (like someone else said, once Joker broke bad, there's no real gray area between general bad guy and full fledged psycho with him).