Falcon666, you've hit the nail on the head. FR keep a presence at LTN to keep EZY out of certain routes and specifically finding the Irish routes very successful, despite having Stansted up the road, they are not likely to leave any gaps going west for easyJet. unlikely easyJet would take them up in any case.
Some selections of routes have been very Strategic, selecting Malta ex LTN keeps North London market to Malta sewn up, same for Morocco routes, easyJet were unlikely to follow FR onto these. So LTN in a sense is niche.
FR avoid EasyJet at LTN as much as EZY avoid FR at STN.