This is crazy. Most "normal" passengers want as quick a journey time as possible!
I accept some enthusiasts will want to be on a train for as long as possible, so will perceive value for money to be based on a longer journey time being considered better, but that's definitely not what most passengers want!
In fact, the faster the journey time, the higher a premium you can charge!
York - Doncaster is about the same distance as Strood - St Pancras. Tickets are not priced by journey time (which would be daft), or by mileage (which they are in some countries) but instead by market based pricing. The market can bear a higher fare if the service is faster and more frequent and the stock is to a high standard.
The York - Doncaster service is very fast, taking 20 minutes, though the timetabled time is typically around 23 minutes, it's faster than Stood to St Pancras on HS1, yet the HS1 fares are actually more expensive.
Despite being slower, Strood to St Pancras costs more, for the same distance, £37.60 for the Anytime Day Return (SDR) which is a mere £17.40 for York - Doncaster SDR. To return a different day requires an Off Peak Return (SVR), that's £27.70 for Strood - St Pancras compared to £21.30 for York - Doncaster.
So I think your post is completely flawed.
That said, entirely separate to the point you make, the York - Doncaster fares have risen massively since around 2001, when the fare was only £5 for an Off Peak Day Return (CDR). In 12 years the cost of such a journey has increased to around 3.5 times the cost! So, yes, it costs too much, but no it is not a particularly expensive journey, as there are plenty more rip-off fares.
But no, I don't accept that a faster service should result in a reduced price
