I agree, but would go further and say your suggested routing of X73 via Burnopfield and Metro centre should be permanent. This would revive link with Annfield Plain and serve Central Station
Tan field could get x70 or  split 6 and new 6A to serve Tanfield hourly , keeping a half hourly service on remaining parts of the route.
Lanchester to Newcastle takes almost 2 hours on #6 !  This would be more popular if an express service was introduced eg. X72 Lanchester, Annfield Plain, Flint Hill, Burnopfield, Newcastle