I've checked the P.V. Inner and outer diameters with the one we used @ Onion some years ago, although we've made mostly drivers.
The last sprocket we did was a Ti 40t for an earlier 1x10 setup in 2012, though.
I understand that any even minimal help is wanted about engagement surface and stability of the assembly, but trust me, the odd spline will add near nothing, even backward. There, what makes the difference, is the width of the insert's base and the locking effectiveness....
The minor diameter determines the contact amount between the side of the splines, that's what engage....the major diameter is what determine the tolerance of the whole insertion. He is right about the 0 negative tolerance, In my perspective, the major diameter positive error amount, has little to no importance, and you can have a .5 positive error without issues. A +.25 error in the minor diameter, though, leads to laxity and mostly to a poor engage, thus leading to wear and dents of both the body and the inserts. Also. from my retro-engineering measurements, a typical wobble in a hyperglide coupling (before to lock it) is about 1.5° or 0.45mm at the splines (35*3.14/360*1.5) that is again in line with his 40°+- 1°.
Agree about the DTswiss ratcheting system....that's an Onyx driver for visual reference about your straight Vs angled splines doubts. The smoothed edges are probably intended to avoid edge dent, a very common issue, and the straight splines give a flat contact surface.
As to the 14t cog, I got it, yes they usually misses some holes annd have unwanted ramps. Why don't you look at SS cogs? they have a wider base, are flat, and often drilled all around, or missing a single hole. Also I think you can get them cheaper...If I well remember Miche makes blank and drilled cogs useful for the purpose.
EDIT found these Point Racing SS cogs at BMO.de, aren't they good and reasonably cheap? If you have a machinist, start with a blank cog and drill out the (supposedly) 44mm BCD 6 holes IS rotor pattern. https://www.bike-mailorder.de/point-rac ... zel-ssp-tx