I think the point about STN is that if their ambitions are for a bigger (Middle East maybe) premium airline (as misguided as that may or may not be) then why would they want to bring an airline in first who will put downward pressure on the premium fares. We all acknowledge that this is where legacy/flag carrier airlines make their profit.
I'm not saying that MAG did turn down la compagnie and it is good that LTN have a long haul service but I can see why STN would. Also the amount of fervent criticism of STN the airline pit out before launch was unnecessary and smacks a bit of sour grapes.
Of course you want to believe LTN is a boutique airport that will see a boutique airline thrive. Only time will tell