If you're coming down short finals at significantly more than that in a light aircraft, you're more likely to over-flare and cause yourself a problem.
This is a very strong statement - I had typed nonsense, but edited that as it was rude.
Also, you haven't allowed for headwind in your approximation of the sink rate required.
In a PA28, you would be at 75kts, less a typical headwind of 10kts =65kts, so a 3 degree slope would require 325fpm, from a distance to the threshold of about 1 mile, which is not sensible in a light single, IMHO. The stronger the wind, the worse the numbers.
I would approach around -600 fpm, adjusting for wind accordingly, giving me a very comfortable and stable approach.
Having got my licence in 1994 and made several hundred (incident free) landings since, I speak from experience, not theory.
Having also operated a lot in a CATZ, there simply was not room to make a 3 degree approach, a 1/2 mile final from 300 feet was normal.
And it's not only light aircraft that can do this, have you experienced the 146/RJ on the 5.5 degree glideslop to LCY/EGLC?
There is another thread about bomber circuits - there is some fit with 3 degree approaches and these.