Are long haul connections via LON that important anymore? Doesn't the MAN route offer that?
LCY is actually quite useful from the Cornish perspective, and could connect to an array of major European business centres and some leisure destinations. Though it perhaps doesn't maximise the inbound potential to Cornwall, so depends what the objectives of the local authorities are.
If course, a FR is is 1/3 full would probably being in far more tourists than the other options