There is another possibility, the killer made it look like there was a huge fight and broke the light fitting on purpose.
That is a possibility Caroline, we do tend to be lulled into acceptance rather than questioning what has become the accepted truth' of what happened that night. In fact if we think outside the box we realise there are other possibilities which are not often considered.
I along with quite a few others believe Nevill was hit when he was already collapsed on a chair, how else could anyone have hit him as hard as would have been necessary, if he was standing? He was head and shoulders taller than Sheila therefore it would have been impossible for her to get near him if he was standing and also quite a good 4 inches taller than Jeremy which although easier would still have been a challenge if Jeremy had tried to bash him that way, because Nevill's reach as well as his height would have been a huge advantage.
This does call into question the whole idea of the 'struggle in the kitchen' imo, including the paint on the silencer and scratches on the stone lintel.
It would have been easy enough to lay into Neil once he was felled but still alive and then to trash the kitchen to imply there had been a mammoth struggle. Considering the suggested strength of the struggle there is very little evidence of blood spillage and spattering.