"That's what I was referring to by my legacy comment. We just don't know how much of that was dictated from external politics or internal thoughts."
Perhaps neither.
Early routes were (mostly) along disused railway lines, which were obviously mostly flat but in places had been cut by developments or reverted to fields, so detours were involved.
Then there were the local authorities' and landowners attitudes, practical (often costly) issues of drainage, missing bridges etc.
When the idea of the Millennium Network came along there was the added problem of making it all connect - complete with unsuitable roads and traffic.
I do get the impression that looking after the current network isn't the priority it should be (but then that would involve revenue money). Perhaps SG should find some more money for looking after what exists (or dealing with improving the bad bits).
"Recent decision making seems better though..."
I think that is true for many reasons. I think there is a better understanding/working relationship with SG/TS - but money (and a sensible share of Transport budgets) remains an issue than SG might be beginning to address.