I’m sure we’ve had this before, and...
1) not all freight from Felixstowe to ‘the North’ needs to go towards Doncaster; indeed not even a majority of it does. A great deal turns left at Helpston.
2) it’s all very well saying ‘short sighted’, but in 1982 the prospects for the line (indeed almost any rural line) were pretty bleak, and it was simply not realistic to expect that Felixstowe would become the traffic generating centre it has today.
Yes we have heard all this before.
Felixstowe in 1980 or so was one terminal (the Landguard one) - the capacity of the port was well under what it is in today's world , with the addition of 2 substantial container handling berths. At the time the practical capacity was 4 20 wagon trains a day from a 2 track loading terminal. A significant amount of this traffic came from the the Stratford area via transfer. There was a northbound Coatbridge liner via Peterborough and not much else. (bar the odd special) - the pre-electric GEML had 1 Norwich -LV an hour and electric services off the Clacton / Walton lines and obviously some peak starters. Capacity was not really much of an issue.
The "Joint Line" was effectively dead in the water - the large flows of London bound gas and industrial coal (that which did not go by sea) - came from the Notts etc non water served coalfields which as far as longer distance flows were concerned had been declining since the 1950's. Traditional gas works and domestic coal burning was very much on the way out .There was no substantial flows of either Speedlink or Harwich bound ferry wagon load traffic - and that was to dissapear in favour of Dover a little later. (and to go completely with the Chunnel)
The glory days of the 1930's when vast quantities of East Anglian agriculteral produce moved by rail had gone , leaving a low baseload of freight - and some of that was seasonal and low revenue - things like sugar beet. The long distance aggregate flows for East Anglia was in the future - and in any case much less than to other parts of the Greater London and South East areas.
The passenger traffic in what was disparagingly called "other provincial" services was yet to see the developments that came later with newer fleet and better marketing.
Finally - BR and freight in particular from the late 70's had very challenging cost and falling revenue targets. Even the bullish and positive Sir Peter Parker had it on his radar as an area of concern. The GN / GE line was a very high cost railway to operate in a not very inspirational business scenario. Closure was not "Short sighted" for the times.