Mike, I came to the same conclusions as you did by very much the same thought process, and was expecting the off road performance to suffer, and resisted a Diesel conversion for many years for that reason .
In some ways it has, gone is the ability to trickle along at 300 rpm and then power up a very steep hill all the way to 2400 rpm if needed, then lift off at the top and drop down to 300 rpm for the decent on the other side.
Tick-over is around 700 rpm when hot now and I need to go up a gear to avoid wheel-spin when the power comes in, which means I have to change down a gear at the top for the decent, which is not so controlled now.
I have recently improved the throttle control by moving the rod linkages in relation to the pivots of the bell cranks, (drilled new holes) this has "geared down" the pedal so any bouncing around produces less unwanted input.
All this is may seem rather extreme for many people reading this, many owners may never attempt such things, and therefore miss the point of our concerns, but the main attraction of Scammell Explorers, WLFs and such, is often the fun to be had off road with them.
As you say it's nice to see other people's opinions