The debate was not about Weymouth to Bristol, it was about whether you pass through Frome from Exeter to Paddington. You do.
Are you saying Castle Cary to Westbury is not the main line into Paddington? If so what in your opinion is? Frome is quite clearly not on a branch line.
Frome is on the fast and direct line into Paddington, between Castle Cary and Westbury. I know because my mother-in-law lives there and the map doesn't lie.