I'm trying to say that for all these new services, if you run them alongside an existing service which is more frequent, then they will not work.
GNE have stated that the service isn't covering fuel or wages and I think this is the reason why.

Take Newcastle Road as an example. Using round numbers for ease, 20 passengers ph will travel between Park Lane and Fulwell Mill using an even spread. With the ratio of buses between the two points at the moment, 4 will use the x3, 4 will use the 9 and 12 will use the 35.
That's using an even spread, which we all know doesn't happen in the real world. Passengers get the most frequent bus between the two points, in this case the 35.
For the X3 to be a success, it needs to compete on an even playing field with alternative services. It can't compete between these two points for frequency and it is arguable it can't compete between Sunderland and Newcastle with the metro for frequency either. The only place it can offer a viable alternative is from Boldon Colliery to Newcastle, hence the introduction of the x36 to run alongside it.

There are countless similar examples of this happening around the GNE area time and time again, more so since the 2006 changes.

Edit.
Looking at it from a different point of view, look at the Arriva X2 versus the GNE 21 and x21 at any point between Newcastle, Chester and Durham.
100 passengers spread equally per hour between the services and there is only going to be one winner if the ratio is 6 : 2 : 1