First, a seating plug does not represent the whole seating die, the seating die does not represent the entire die set.
Bullets profiles differ - a lot - and no seating plug can possibly 'fit' the ogive of all bullets but there are several simple ways we can tweak them to perfectly accommidate any bullet we may wish. Anyway, small seater plug rings on the ogive of a bullet looks odd but generally make no difference at all in effect.
Statiscially, a single test sample of any manufactored product proves nothing. I have a lot of conventional dies of all brands and many cartridges, some are better than others but they are all good so, after some 45+ years of reloading with dozens of die sets, I have no favorite brand (but I did when I was still green and it was Lyman). I soon learned to select individual dies from different sets to make the die set I want and that almost invariably requires a mixture because, on average, I have found no brand of dies or sets of dies to be automatically superior to any others. There is no assurance of anything simply by the cost or color of the box, I've found as much variation between individual dies of the same brand as between brands.
(That's for conventional die sets, the two specific exceptions to that general rule are the competition sets from Forster and Redding. However, the advantages of them are not great and vary depending exactly which individual die they are being compared to; a "good" conventional set will do as well as a vastly more costly set. And the most perfect die set ever assembled will be negated by sloppy user technique.)