User choice
I have looked at where I have flown from and to in the past 6 months and I have used SEN, LCY, STN, LGW, LTN and LHR. When analysing why I chose the airport that I flew from, in every case but 2 it came down to the destination I was flying to and the time of departure. I chose the airport not because of the airport experience but because the flight I wanted to be on left from that particular airport. Granted, most of my flying was long haul but I also did a good amount of European flights and some domestic in the past 6 months.
I took two flights that I would have preferred to have flown from SEN; one was to EDI and the other to DUB. Both departed and returned to STN and I would have preferred to have not driven for those particular journeys.
It is great that SEN has a fantastic customer experience but I don't think passengers will use it because of that. They will use it because it has flights going to destinations that they want to get to departing at times that suit them. A good example of this is when I fly LGW to GVA. It would be easier for me to fly from SEN but the SEN flight leaves in the middle of the day; no good to anyone who has to work for a living.
As for short train to terminal transfers I think London City gives SEN a run for its money. As do the LCY short and long term car parks. Where LCY scores highly also is the well managed security queue and the quality of the airside retail/catering that SEN just cannot match at present.
Let's hope that the continuing Which appraisals give SEN the publicity it needs to stay in the limelight. However without meaningful routes at decent departure times the airport will unfortunately continue to struggle.