I found even the slightest issue with ignition timing, plugs & points, or idle mixture can make hand crank starting difficult. Had this issue with my S1 when in France & my starter motor packed up. Towing or Bump starting worked but not Hand Cranking. It was the carb setting had drifted and the timing was slightly out.
I haven't looked but I think i asked the grenadier folks if they put a crank on it. I'm sure the new landrovers do not. and the Defender, IDk but cranking a v8 ........ you need your wheaties! the WW2 half tracks could be hand cranked, my dad said there was always some big guy around that could do it!