Neither STN nor LGW have any kind of BE route network for them to offer connections to as that all moved out of London or to LCY, so neither has any particular advantage over the other. Ground transport time is pretty much the same to central London if that is the final destination.
As a point to point then STN is a little far out, perhaps LTN would have been a bit better, but how cost effective that would have been I don't know. It's clear LCY wasn't making money for previous operators, but perhaps if they gave it another go and offered connections through there then it might work better? I know cityjet had a similar set up and that ultimately failed, but perhaps BE could make a better go at it? They are a bigger brand associated with lower costs.