I think those estimates are very high. What you are implying is that on a 5 quart sump there can be anywhere from 1/2 to 1 quart of oil left in the engine. Only leaving the filter on would you have that much oil left in the engine.
Agree. . . seems a bit high but possibly on some engines. Not all have turbos and/or other areas where a lot of oil would remain. Speculating on how much oil remains in a particular engine, is just that.
Besides as another example . . many Harley motorcycles have about a 2.5 quart oil capacity with a "dry sump" crankcase. The "dry sump" and connections can hold 1 quart or about 40% of the oil still in the bottom of the engine when oil is changed by draining the separate oil tank and changing the filter.
There are ways of doing a FVOC, but most owners and Harley dealers just drain and fill the oil tank. Now that is a kind of worse case scenario. The point is, those cycles have been doing fine with the recommended oil changes.
I suppose if an owner wants to max out mileage and longevity go for a FVOC. However, there are owners of +2010 cars and trucks ( with GDI engines) with over +150K miles on the engines and the engines do not use significant oil with doing reasonable and regular oil change intervals. In other words, not going down to 0% on the DIC Oil Life Monitor. I do not remember going any lower than 30% and most often is above 40% at 4K to 5K miles when I normally do an oil change.
And I always drained the Equinox and all my vehicles level . .. remove the drain bolt and lower to let it drain or even tip it with the jack a bit towards wherever the drain bolt is on the oil pan.
Even with full Pennzoil synthetic and changing the oil every 4K to 5K miles, I've had a few Blackstone UOA and metal and wear is well below their safe figures with fuel dilution well under 1% as reported by them on our 3.6L V6 2015 Equinox.
It would seem most owners would do fine just observing a good traditional oil change regimen. No need to scare people making them think regular drain and fill oil changes aren't sufficient.