I?ve noticed this too that the Saturday SWR» timetable is better than the Monday-Friday timetable on some lines. So yes maybe Saturday is the new peak for travel by train these days.
Not just SWR ... TransWilts through Melksham is back up to 100% on Saturdays, and 88% on Monday to Friday - not as dramatic as Bookham, but still leaving a gap in the early evening - if you miss the train just after five thirty from Swindon (a good after-work train for central Swindon), you'll be waiting until quarter to nine for the next and final one of the day.
How are other
GWR▸ lines doing? Severn Beach? Exmouth? Gunnislake? Falmouth? Missing services on locals in the Bristol area?