I know that. Its also nowhere near as important as Sheffield in terms of population size, business links etc, so that needs rectifying. Doncaster a historical beneficiary of railway geography.
As for the rest of your post, I dont think anyone is throwing money at the infrastructure, there are no line upgrades here or money being thrown at it,, its just ONE operator running TWO trains a day. Its still going to be hamstrung by the low speed limit on the Retford-Sheffield section. It just so happens its still quicker going this route than using the MML, which is a shocker in itself.