A quick check on the Citalia website shows that using LGW as the baseline, SEN departures are about 5% more expensive and LCY about 20% more expensive. I would think that those figures make SEN quite an attractive proposition taking everything else into account.
Certainly not. Citalia is a PREMIUM Thomson product which sadly EZY is not. Citalia via BA from LGW will win every time with the majority of their clients.