Point 1
The 'scale' strategy is a good strategy for an LCC airport close to London, but: it is hard to imagine where exactly those additional 2.5m pax are going to come from to reach 5m by 2022. For simplicity that would mean easyJet effectively doubling their based aircraft from 4 to 8. It would mean Ryanair basing 6 aircraft. And it would probably mean the addition of a few more foreign LCC's into the airport. An airport of that scale poses a significant threat to STN.
Does everyone believe this is really possible? Surely more LCC's at yet another London airport is just diluting the entire system meaning less yield and less real income for SEN. The lower the fares go the less profitable each passenger becomes. The only reason an LCC would go to SEN is lack of slots elsewhere and lower airport fees. I doubt STN and LTN are at capacity yet are they? They make a killing from car-parking revenues which allows them to keep aeronautical revenues low. SEN doesn't have this ability as far as I can tell.
Point 2
Regional carriers are a dying bread due to fare levels and fuel bills. Loganair and 'Connect' Airways would earn more dosh by consolidating at LCY where the air fares can be absorbed by the market. Those fares cannot be sustained at SEN.