It is, of course, very expensive to have trains on the fleet that are only used for a small part of the day, and one of the big ways to reduce this expense is to reduce the peak.   It happened in the 1960s and 1970s with the reduction of seaside trains on summer saturdays, and First now appear to be doing it (and continuing to do it further in december if you look at the current edition of Rail) with the peak hour services into Bristol.

There is, though, a difference between what an annual tripper will put up with, and what a daily commuter will take.  I'm not a psychologist, but I note that the daily commuter is a stoic type who will, however, be a lot more of a "problem" once he gets rattled that an annual riviera tripper would.

There's evidence that the current tough commute conditions were intentionally engineered - or at least that warnings given by people who already know the service and flows very well weren't taken into account anything like as much as one would wish.   Remember the official view from certain senior civil servants who used to work for First  that a 30 minute stand is perfectly acceptable.

Now - to be fair to First - they seem to be looking (again?) at best use of trains in the critical peak times, inclding some "out of the box" options which weren't previously possible - using trains that were used on one of the three elements that came together to make up the new FGW^▸ (First Great Western) to support service that came from another element.

I understood the additional diesel hauled service was rented 'by the hour' and was affordable for the times it ran as a suppliment on the Friday. There is still some info on the old Fragonset website, albeit the company has finally gone into administration.

http://www.fragonset.co.uk/archive.htm