Current under 25 selection seems more than ample.
Insurance is also not purely on engine power or size, it’s also about repairability, cost and availability of spares. They also have no option but to accept people who lives in a very high insurance risk area as well as those who in a very low risk area, all at the same cost to the client.
That would never happen elsewhere.
Typical premiums for a mediocre car for an under 25 non motability client seem to be around the equivalent of 6 to 9 months mobility allowance, especially for £20-30k cars.
Just stating facts.