There is some VAILD points been said
Yes people that will travel regularly to the USA many already have points with BA and KLM etc and it will take time to get those people to transfer.
Also 6 months notice of the route may not be long enough as people may have already booked there flights.
I have been looking at the seat plans for Glasgow also and last week they had a bad week also with loads around 60% and they are normally around mid 80%
Think we need to give this route a chance and like what's been said we don't know what the break even is and we never will
Also the business class is starting to fill up so people are transferring hopefully from BA,KLM it's just taking time