Can’t say I’ve ever looked at the GNT in much detail (or anything else similar like An Turas Mor for that matter) but having done The Badger a couple of times in both directions I’d highly recommended it.
I'm pretty sure I looked at this by overlaying both in RWGPS
GNT uses the ATM route for that bit. Also be careful which ATM route you use - the single file one has the harder HT550 section in the north whereas their Day 1 Day 2 etc files have the easier option without the hike a bike up the river
How do TBD and the Great North Trail differ, aside from the diversion to Inverness of TBD?