AvGeek1
How do you know that they are performing better than at STN?
As you say... Munich, Naples, Split, Dubrovnik and Bodrum still operate from Stansted - in some cases at a higher frequency than they do from Luton. That says all you need to know really.
There is room for both airports in some cases. Of course LTN is the focus for EZY's growth and that's why you're seeing those routes introduced from LTN as well. As they do so, that is bound to have some impact on the size of their STN network.
In the case of CPH, that moved over to LTN completely and look how that one's turned out!!