I respect that you think that, but its probably not true. And it certainly isn't true of all luthiers, especially ones with a backlog of work. And it definitely isn't true for problem necks with a twist or other problem.
The only reason someone would ask to have a plekked guitar hand leveled is because a problem developed. Developed.
As I said earlier, the "problem" with plek is that it doesnt stop the hands of time. Minute changes to the neck will eventually wipe out that last 5% of accuracy.
I have hand leveled all my old guitars and been happy with my own work. But there are some things the plek excels at. One of them is that it removes the absolute minimum of fret material. I have an old guitar that is "getting there". I know I can get another couple plek jobs out of it, but if I hand level, it will not last as long.
With a hand level, you straighten the neck, level it flat, and you are at the mercy of the relief the neck develops.
With a plek, the measurement is done under tension and it can cut a fret profile that comprehends the actual curve or twist of the neck. With good necks many probably won't tell a difference, but with marginal or bad necks it can make all the difference. How can you not see that this is superior?