I really cannot see KLM starting Amsterdam flights from Southend whilst easyJet is on the route. It was rumoured in the local press a few years ago that KLM was in talks with the SEN
over flights, however that never materialised, and the oppurtunity for them has now been missed.
In an ideal world, KLM would be on the route, as without easyJet, with the vast connection oppurtunities it could facilitate . However easyJet is now on the route providing an awful lot of capacity (312 seats in each direction a day.)
So to say, if easyJet wren't on the route, a Fokker 70 is too large, is probably incorrect, since a thrice daily Fokker 70 service would provide only 240 seats in each direction a day.
However this is all academic, since the two carriers wouldn't in my opinion be able to co-exist on the route, at least at the moment.