Skyman, Thirty to fourty years ago the road links to both airports were fairly similar. Flights to and from both airports were similar, although NCL did have the edge. This of course you would expect as NCL was a dedicated civil airport a long time before RAF Middleton St George became Teesside.
The big start for the NCL lead can probably be claimed by Jim Denyer. He was in charge at NCL from the 60's to the 80's and he made a lot happen in those days. I agree the loco's are only recent arrivals at NCL but they came because of all that had been achieved by then.
Teesside would now have a long struggle to catch up but if they made the moves I previously mentioned, I think they could make start.
The problem they now face is that the local autorities have decided that NCL is the airport of the north east and laid in the infa structure accordingly. It would now take a real good manager at Teesside to talk the authorities round into doing the same for them.