the wrong Oxford-Reading trains stop at Didcot.
Which 'wrong' trains would these be? The ones that don't stop are the
FGW▸ fasts and
XC▸ , which, in the case of South Coast services, are overcrowded much of the day.
And I think you might find that post-electrification, there's a bit more than 'tweaking' of the timetable. A complete recast more like, to take account of far superior acceleration.