Limiting the weight and power of bikes that new riders can ride won't stop *all* crashes, but it ought to help.
Problem is that the government is notorious for screwing up anything they can get their hands on, and I wouldn't expect this to be any different.
"You have to pass the test on the same weight/power classification of motorcycle that you wish to obtain a license for" is perhaps not an unreasonable concept. No time limits - but your basic written exam should only grant a license for scooters, <250cc, lightweight bikes, etc., and if you want to have a license on something bigger then you have to pass the road test on something bigger - and it needs to be a real test.
The classifications need to be both horsepower based and weight based. An 800 lb touring bike or Harley might not have much power, nor a good power-to-weight ratio, but that much weight can get away from someone in a big hurry, even if they aren't going very fast.
The recent crop of bikes with 40-something horsepower - CBR500, RC390, R3, Ninja 300 - are all in answer to a revamp of licensing across Europe. These are all a middle-licensing stage; one step above 125cc and one step below an unrestricted license.
In conjunction with that licensing revamp in Europe, France is being forced to revoke their long-standing horsepower limit - because it was found to not accomplish anything. BUT. You have to remember that it was found to not accomplish anything within the scope of THEIR existing licensing regime, which already doesn't allow someone to jump on an unrestricted bike without going through their licensing regimen. In other words, for riders who already have a certain amount of experience behind them, the horsepower limit serves no safety-related purpose. It does NOT say that a 16 year old freshly-licensed rider is going to be a safe operator of an unrestricted Hayabusa, because their existing licensing regimen did not (legally) allow this combination anyhow. The most that can be said is that there is insufficient statistical data about that combination, because it has not been allowed.