I don't believe either Strasbourg or Tenerife North can (even in normal times) support a 180-seat aircraft to London. Ryanair has tried both routes from London, and Iberia tried TFN-Heathrow
Gatwick's charges are heavily weighted to favour 150+ seat aircraft at the expense of airlines flying 80-seat aicraft - hence why Flybe left Gatwick. I'm thinking specifically of a Volotea B717 or a Binter E195