Dash&Thump
Your theory doesn't hold water as far as the Wednesday SEN-JER route is concerned.
Flybe have pulled it from 18 June to 4 September, when it is reinstated. To pull a leisure route for the whole of the peak summer season, when the only alternative is to rebook on the Saturday flight or travel to LGW for a Wednesday flight, and then reinstate the service at the end of the season cannot surely be for the reasons you are putting forward.