SWBKCB, I suspect BA probably do know that, just as much as I suspect you're quite deliberately trying to be awkward
Heathrow Harry, they're all pretty small, BACF's largest aircraft doesn't even have 100 seats. So realistically we're talking about having to fill half of what currently goes into Heathrow. I really can't see any issue in filling a few Embraers especially if Heathrow rotations were swapped for City rotations.
I can understand the scepticism. London is, after all a very niche, exotic destination and London City airport... Don't get me started, big inconvenient mess of a place in such an inconvenient location I can't even understand why they built it there in the first place!
It's not bloody Timbuktu!