Re the light bikes/heavy bikes for offroading-
IIRC in the "long way round" they crashed a lot on the 1200 GS bikes. In one slippery section in Northern Russia one bike went down about four times in 1000'.
It eventually sustained too much damage and was sidelined. The Producers managed to buy or rent a small Russian bike to use instead, 125cc or so. It was low and light. No more crashing.
I ride a Maico 490 off road (100kgs) or an Ossa Mick Andrews Replica (88 kgs)
They are both quite decent, however the Ossa is best in the really tough stuff as it is lighter and lower than the 490, plus low geared with lots of grunt. The 490 has explosive power that is not always what you need.
I'm not sure where the idea came from that a very tall 250 kg bike with high horsepower was the right design for offroading. Most of those big tall ADV bikes aren't going to get used for serious offroading. They spend their time rolling down paved highways looking like could go offroading if they really wanted to.