The problem is that "support a person" is also a moving target that is ever inflating. Additionally, distribution inefficiencies (whether you're inclined to believe the bad actors are big government, corporations, or the "1%") also keep moving that target.
Look at it this way. Per-capita GDP has gone up over time yet poverty rates have stayed fairly fixed over the last 40 years.
See also processor speed vs desktop snappiness over time for a similar example of where the underlying performance drivers may look great but the end result appears to stay the same.
It's not a specific percentage because it does fluctuate (not going to look up what it's based on just now), but effectively it will never be eliminated. This is precisely my point to the original poster who postulated that increases in worker productivity were making it easier to support those not working.
Look at it this way. Per-capita GDP has gone up over time yet poverty rates have stayed fairly fixed over the last 40 years.
See also processor speed vs desktop snappiness over time for a similar example of where the underlying performance drivers may look great but the end result appears to stay the same.