Just curious where your data is coming from? It does seem to align with what I would expect in those designs but I like to ask. I'm sure OEMs have toyed with the toughness/hardness to figure out what's needed. Obviously a pin fracture is simply not acceptable. I would also personally want to make the pin the primary wear item as it needed to maintain some ductility anyway.High quality pins are typically made from medium carbon steels, or chrome-moly steels. The core of the pin is typically 80-100-ksi yield strength. The outer 0.100" is induction-hardened to between 45 and 50 HRC. For extra wear resistance, and protection from the elements, they are sometimes plated in chrome (72 HRC). The pin has toughness for impact-resistance, while the case-hardening provides applicable wear resistance. If the pin were through-hardened (like bushings are) the pin would fail from impact-loading (brittle fracture) in short order.
High quality bushings are typically made from air-hardening tool steels (similar alloy to what iron worker dies are made from). The bushings are machined from annealed round-bar, then heat-treated (through-hardened with light-temper) to between 50-55 HRC. Note that bushings can still fail from brittle-fracture, but it takes appreciable abuse. The hassle with these types of bushings is that the bore interference-fit must be nuts-on (normally requiring line-boring operations). Large bushings are often installed with shrink fit (liquid nitrogen bath). Smaller bushings can be pressed.
If you do the math for a typical excavator/dozer pin joint, the compressive stress easily exceed 80,000 psi, which is beyond yield for most steels. Non-case hardened 4140 pins (30 HRC typical) will not last nearly as long as case hardened pins (extreme-pressure grease is your friend).
A good source for induction-hardened chrome-plated round bar for DIY pins (both US and metric sizes) is CRConline.com. The normal application for this rod is hydraulic cylinders, but this stuff works great for pin joints also - provided you don't have to drill any grease holes through the induction-hardening. If you need to drill a grease hole, you need to grind the hole through the induction-hardening, to expose the softer core of the steel - which can then be drilled/machined. This type of rod is generally considered non-weldable (too high of carbon content - welding will compromise the heat-treatment at best, or initiate cracks at worst).
I cannot say I've ever run into a pin with plastic deformation defects which would point to the softer side of the curves.