I come from a background in off road driving and have owned Defenders most of my driving life.
Always ran 265/75 tyres and never had many issues. We had bad snow one year and got stuck on a drift, drop from 30 to 15psi soon had me going again. At that pressure on those tyres you float on the snow rather than dig in.
Friends with me had 235/85 and didn't need to drop pressures as the tyres dug in and cut through the snow. Their vehicles had to work a lot harder though, constantly cutting through rather than me floating on top.
Now mud was a different story, thinner tyres cut through and find the hard ground underneath. My wider tyres left a lot less damage though on sensitive areas, as again they'd float over the top.
Now we don't all have the luxury to safely run around at 15psi on roads in cars, so I'd agree for snow the thinner the better to get down and bite the hard stuff when you need it!