What it really shows is that perfection is not needed and wouldn't really improve things.
I have been loading for 40+ years, so I a wide assortment of dies.
A couple of years ago, trying to load .38 Special Wadcutter ammunition as accurate as factory loads, I started to compare different dies. Found the two seating dies that seemed to consistently produce the best accuracy were the Hornady New Dimension seating die with the alignment tube and the Lee seating die. The Lee die didn't even have a seating stem that matched the bullet as well as the Redding, RCBS, and Dillon dies, yet the rounds seemed to be 0.5-1.0" more accurate. Found that the only roll crimp die that improved accuracy was the Redding Profile Crimp die.
The Hornady New Dimension sizing die seems to go lower on the case and sizing more smoothly than the other carbide dies.
The expander die that seemed to produce the best accuracy was an OLD RCBS expander that could expand the whole length where the bullet would be seated and didn't flare out the case but simply sized the case mouth section to about 0.365". The other expanders, including the various Lee, Hornady, and Dillon powder-through expanders and the Lyman M-die expander were all pretty much the same in average accuracy. The key appeared to be having an expander large enough that the case ID over the length where the bullet would be seated was ~.359", using the Remingtion 148gn HBWC that measure 0.360-0.361" at the skirt. If you swaged the bullet down at all, you get mediocre accuracy.
This led to me taking out the sizing die. The cases don't expand hardly at all at the low pressures the loads produce and this leaves the case ID just about exactly what is needed.
My opinion is that Lee makes great dies, but it is fun to mix-and-match and see what effects you can find.