Re the 71. It just runs backwards and forwards all day as a stand alone service.
There were comments on the old gne facebook discussion board about linking it with the Seaham bus.
My thoughts are that as it was/is - it is neglected. Passengers for however many years along the route, were used to a decker continuing to Hartlepool or Newcastle as a 231, 735 or 21a for however many years.
Curtailing it at Chester le Street and stopping the Sunderland section of the route seems to confirm my thoughts.
There isnt going to be another bus from Chester le Street to Newcastle, but passengers are left with an substandard service in the mean time.
When the ex-london darts were used, GNE found that the service suffered with overcrowding, so introduced the mpd's onto the route and then in turn reduced its mileage. Make what you can out of that.

Re X10 to Leeds. There did used to be a Northern service to Leeds. But as pointed out, a train would be quicker and tacho laws nowadays would restrict driving hours.

RE X7. I said weeks ago, that if GNE were so determined to make this a success, newer buses would have been used.
As it is, spare vehicles from the fleet have been alocated and despite them being reliable engines, seem to be having problems. Parked up in a layby last week, one screamed past me up the incline from Castle Eden on its way to Peterlee.
If GNE continue using these vehicles, then passengers are not going to build up any loyalty towards the service. Missing Dalton Park was a mistake, using unsuitable vehicles is an even bigger mistake