The big thing to see here is that the innermost part of the splines adjacent to the tapered face that seats the wheel NEVER WEARS OUT! Its like getting a free go/no-go gauge with every wheel!
See that section about 3/8”, wide right up against the taper? That’s how the splines were shaped when the wheel was new. The splines are wider and rounded on top. The outer segment of the splines where the crests are thinner, nearing being sharp are where the hub drives the wheel, both going forward and stopping.