I agree wholheartedly that the 3 deg approach is inappropriate in SEP aircraft. The 'runway aspect' should be used to assess final approach angle, NOT reliance upon 3 deg PAPIs/VASIs.
As an aside, when CFS came to do their annual visit to the better UAS at Benson, one of their Jet Provost background people queried why we weren't flying 3 deg approaches. It was pointed out that the standard Bulldog circuit (using that '45 deg rule') resulted in a steeper approach path. He was sceptical, so I did some calculations based on the '400 ft point' which they insist upon and proved that the resulting approach angle would be 5.4 deg. He then admitted that he was wrong; I also showed that if he really wanted us to fly 3 deg approaches, then the '400 ft point' would have to be renamed as the '222 ft point' - an absurdly low height to roll out at on final for a basic student.
Leave 3 deg approaches to those with more than one engine - or with a bang seat! The 'dragging it in from 2 miles out' approach one meets at places like Kidlington is wholly WRONG for a SEP aeroplane!