Sorry Crab, whilst you are correct that fewer singles fly over congested areas, that doesnt prevent 'legitimate stats'
All we need to know is the number of times a single has to make 'an unavoidable landing or ditching' per unit hours flown and the number of times a twin has to do so.
If singles make more such landing in the same number of hours, then it is irrelevant whether the data has been taken from singles flying over cities or uninhabited fields - the aircraft doesnt know what it is flying above
The debate that then needs to follow, if the number of forced landings is less for twins, is whether the reduction in such landings justifies the increased cost and restrictions. That depends on the risk to life of such landings (not so easy to specify) and the willingness of society to balance that risk against benefit