@BigDaveK, the difference is barrel aging. I wanted barrel aged wine for the port, but have no need for 14 gallon of port.
It's a matter of scale. For a Port house which makes thousands of gallons per year, they produce many 225 liter barrels of port, and blend to hit one of possibly several targets.
For a home winemaker who wants 4 to 8 liters of port, it just doesn't work. I took 6 bottles of wine, backsweetened, and added EverClear 151 to hit 20% ABV.
The number of batches I'd have to cycle through in a small barrel in 3 years is daunting. I barrel age my heavy reds for a year, so it would take 3 years before I was in a position to age the Port wine the way I want.
Although, the tiny barrels (in comparison to my current 54 liter barrels) wouldn't take as much time to get the concentration that requires a year in my current barrels.
Bottom line is that it's a nice idea, but I don't see it working. I don't see a way to produce exactly what I want, although again, the experiment is worthwhile, and I'll probably do it again.