The Sunday service in IMHO▸ is awful. The First "Bristol bound" train leaves in the Afternoon. Considerably less than ideal and the last return to Frome being 20:49 (Bristol Temple Meads - Weymouth Train). Not great really.
I quite agree with you thetrout that the Sunday service at Frome is poor, although not quite as bad as you suggest - the first train to Bristol leaves at 0925 (0939 from 8th December). Granted, miss that and it's almost a six hour wait for the next one.........
Some good news for any Christmas shoppers is that an additional train is running to Bristol leaving at 1101 for the next three Sundays