I can sympathise to some extent with the idea of a tiered licensing system for motorbikes since few new car drivers can afford to go out and buy (and insure) a sports car but many can afford a sports bike. Unfortunately, whoever comes up with such systems seems incapable of doing a halfway decent job.
It was bad enough under the previous regime where new riders were limited to 33 bhp. It sounded sensible on paper but there weren't actually any suitable bikes being sold in this country. You had to buy something pretty ancient, likely with clapped out suspension and brakes. Super safe.
Since manufacturer's claimed power outputs don't actually correlate well to
real power output you also ended up trying guess the real power of a prospective bike and factor in a loss of horses over the decades of use the bike had had at the hands of feckless teenagers. Or you could do what almost everyone did, which was to ignore the restriction.
I was a good boy and bought a bike that came with restrictors and a dyno-testing chart from a garage. At a hefty premium of course. Only later did I realise that the thing was a complete fabrication, such was my naivete.
Insurers would sometimes ask for proof of restriction. Unfortunately there was no such thing, no recognised certificate or certifying body, so what you would do is write as official-looking a letter as you could to the theme of, 'This bike is restricted, honest.' and cap it with a fancy signature.
The new system is far worse. There are 3 tiers of licenses, each with multiple conditions. The restrictions no longer lift automatically after a certain amount of time and the practical test for motorbikes is in two parts, meaning that a young rider looking to progress gradually must do the CBT, then pass the theory test, then pass
six practical tests over 4 years. The last four require you, in practice, to rent a bike off an instructor which is likely to tip the total cost into the thousands, especially if you fail any of them.
And if all that doesn't seem egregiously retarded enough, there is currently no reason for a 17 year old to take the test! Amazingly, those transitioning from the CBT to the first license tier are still limited to a 125cc bike. That means the most financially sensible thing for a skint teenager to do is to spend two years riding around with no training until they turn 19, or to keep retaking their CBT until they turn 24 and get the whole test over and done in one shot (3 actually).
If you've bothered to read this far you've probably come to the same conclusion I have: either those making the law are trying to kill as many teenagers as possible, or they are the sort of people who would be unable to locate their bottoms with both hands. If they actually wanted to save lives they would, as
@User76022 said, abolish the CBT and make people get proper training by proper instructors.