Let's do a mileage sum on this.
31 Oxford-Bletchley
20 Bletchley-Northampton
12 Northampton-Wellingborough
25 Wellingborough-Manton
22 Manton-Peterborough
45 Peterborough-Cambridge
Total mileage 155, twice as far as the route via Bedford.
Yes, I allowed myself to run away with the argument(s) and ruin both.
What I should have said was: I think the closure of Northampton - Wellingboro was a tragic loss, and should have been kept back in 64.
Not for a mere Northampton - Wellingboro shuttle, but for a Northampton - Corby service, or, possibly, a Class 2 service to Leicester, allowing Desborough and Kibworth and possibly Wigston Magna to stay open. (But I would prefer Corby myself. And that's v much on topic for this thread.)
Fast forward to the 1990s and talk of Oxford-Cambridge.
This would have developed into an argument that rather than Oxford - Cambridge, a better option would be an East-West route Oxford - M Keynes - Northampton - Wellingboro - Corby - Manton - Peterboro and probably then Ely and Norwich.
This would definitely be sub-optimal for Oxford - Cambridge, and obviously would not be able to serve the Tempsford - Cambridge line as proposed today. But this serves Bedford and nothing but a commuter section from Tempsford into Cambridge. (And Wixams park, at some stage, we hope. But that was far away into the future in 1995.)
A route via Manton, however, though still somewhat indirect, links far larger populations than Bedford and the Tempsford corridor.