The classification system is actually a leftover from that brief, halcyon time when our ancestor’s civilization and Ultrahumans coexisted. It was an attempt to categorize Ultra gifts, basically to let people know what a given Ultrahuman might be capable of.
There weren’t, originally, supposed to be just 3 categories. In fact, they didn’t want to do categories at all. The design was supposed to measure Ultras output, speed, etc, just like they measure everything else. Instead of ‘Ultra Speed 2’, you’d have a top speed in kilometers per hour. Instead of Ultra Strength 1, you’d have the amount of force they could put out.
What went wrong with this scheme was that Ultra gifts didn’t cooperate. An Ultra’s strength didn’t seem to be a consistent amount of pounds per square inch, it was maddeningly inconsistent. The degree of force an Ultra could output seemed to be affected by how difficult it LOOKED, rather than how difficult it actually was. An Ultra might heft and throw a car with all of his effort, but easily shove aside a small cube that was actually considerably heavier.
Speed and Durability was similarly vexing. An Ultra could outrace things they thought of as ‘fast’, but their time when they were doing what they thought of as their ‘top speed’, didn’t really bear any relation to what they could put out when they were needed to.
Ultimately the 3 tier classification was simply an admission that that was as granular as they could get. It’s a lousy system of measurement, and the borders are extremely porous (particularly in Ultra Speed, where reaction time and top speed are only loosely related). A strong 1 may be stronger than a weak 2. They were just both initially categorized wrong.
Our own Union, of course, has a far superior method of categorizing Ultra abilities. But spreading such a system would be to squander an advantage, and in such trying times our leaders have decided that we cannot afford to do so.