Gabe, for years I've looked for some kind of comparison that would shed light on the tiered motorcycle licensing question but haven't been able to find one. Even a UK/US fatality rate comparison--where licensing is just one of many uncontrolled variables--is ambiguous. At a point in the '90s our fatality rates were similar, but then motorcycling took off in popularity in the US and the influx of noobs pushed the US rate higher, whilst the UK rate stayed about the same.
There is actually a useful bit of evidence related to tiered driver's licenses for 16-17yos in the US. A few years ago the safety establishment trumpeted lower death rates in states that had adopted much stricter licensing requirements for the youngest drivers. But a close look at the data
nerd) revealed a more nuanced story. Fewer 16-17s were dying in those states, and the rate per population had dropped too. But the rate
per licensed driver stayed about the same. My interpretation is that by creating a licensing process that was more difficult to navigate, they had reduced the number of licensed drivers, but they had not preferentially excluded
bad drivers. The basket was smaller, but the percentage of bad apples in it was unchanged. That's part of what I would expect if we were to adopt a tiered motorcycle licensing system: Some people would be discouraged from taking up motorcycling due to the process, but those who endured it wouldn't necessarily be safer.
One question underlying the tiered licensing issue is this: Can you train the stupid out of a prospective rider? I know you can overcome ignorance with training. But can classroom discussions and range drills turn those few reckless idiots into responsible riders who accept their own mortality and eschew potentially deadly risk while still enjoying occasional high-speed fun? My hunch is no. I have 3500 words on "The Potential and Limits of Training" here somewhere that I've never posted because it's such a controversial topic.
That said, I'm a huge fan of learning to ride on a small motorcycle. I started almost 30 years ago on a CB900F and a few years later got a Yamaha FZ750 (their Superbike entry at the time). But I didn't really learned to ride until I got my Hawk GT in the late '80s. There's just something about a small, light machine with an upright seating position that makes it easy to learn how to push the bike toward its limits.