That can be turned round to remove the detrimental implication - "EGTs drop rapidly under light loads" - it's a feature of diesels running unthrottled turbo-boosted air and controlling power output by varying the fuel injection quantity and boost pressure - the excess air cools everything.
Indeed. I should have been more specific. I meant compared to other more modern diesel engines, my ALH, BHW, and 1.6td powered vehicles see higher EGTs under much less load and faster than Dmax or CTD. I imagine the BKW is similar to BHW but I don't have a gauge on it to know for sure. "excess air cools everything" is a good point and the reason why higher RPMs when towing help keep EGTs down. I am no expert, just speaking from my own experience. "EGTs drop rapidly under light loads" is also a good point but you have to climb the hill before you can go down it.