To be absolutely objective, the Saturday based timetable and the ENCS, are independent. In Wilts, they have chosen to offer the free fares at all quieter times (whether working weekday, bank holiday or weekend) - but just because the bus company is running to weekend times, doesn't mean that it's 'off-peak'.
In practice of course, most of us think of the holiday as starting Friday 21st December to Monday 2nd January and expect fares to charged to bank holiday rules. I'm not sure what the financial implications are for the councils/central government and for the operators (ENCS travel is refunded at a lower rate than fare box prices) but I'd rather a Saturday bus service throughout the period with chargeable early morning buses, than no buses at all.
You're totally right that the timetable choices on commercial routes and the
ENCTS▸ funding decisions are not syncronised, just as ENCTS funding even at normal times has anomalies. There's a legal requirement for ENCTS to be provided at certain times and there are "bare minimum" councils. There are also more generous ones, and ones who are pragmatic in providing extensions to help make bus operation more viable - ask me on a day that's not Christmas Day to talk about the 09:00 v 09:30 start.
Which is not to stop you, me, or anyone else with an interest suggestion some sort of harmonisation. Old problem being that neither the local authorities nor the bus operators really believe that Joe Public who uses the bus actually understands bus funding and accounts, and that both believe that Joe Public is typically interestedly in HIS local bus stop and where he goes on the bus from it. Sadly, without too many bus user groups, Friends of a town's bus stops and community bus partnerships, the local authorities and bus operators are all too often correct in their reading of the knowledge and motivation of the "campaigner".
Interestingly, rail journeys I looked at for 27th December on GWR▸ were off peak all day. Whether that is to compensate for the reduced service due to eng works or just an attempt to get more seats in use at a quiet time, I don't know.
The whole week is off peak / super off peak. You can be assured that it will have been looked at commercially rather than as providing compensation. It makes sense with a very high proportion of potential leisure traffic which is likely to be cost sensitive during that period to encourage it, and it would probably be a very poor piece of
PR▸ to charge anytime fares during what - for most of the office population these days, I suspect, is in effect a public holiday.
