It's our adversarial justice system, everybody gets their day in court to argue their point, if they wish. Many continental countries operate an inquisitorial justice system which sees things differently. Presumed liability obviously saves time.
A local cyclist was slipstreaming a bus a few years ago, the bus slowed to turn left, the cyclist, sprinting head down, collided with the back of the bus and died. Under presumed liability it'd be the bus driver's fault, he had no knowledge the cyclist was so as he couldn't see him in the mirrors.
I'm sure presumed liability does not operate without certain caveats. Adherence to the law would be one - i.e. riding at night with suitable lights and reflectors, obeying traffic signals. Maybe even mandatory cycle training, compulsory insurance and helmet wearing too.
This is just misconception. Firstly, presumed liability wouldn't be assumed for criminal proceedings, only civil (ie. payment of insurance typically). It wouldn't be the bus driver's fault under presumed liability any more than it is the driver's fault now. It is simply the presumption of liability for payment of insurance.
We have ad-hoc presumption of liability in motor insurance cases now. Such as in a rear end crash there is a presumption of liability on the person crashing into the rear. But in these events, liability can still be determined on the nature of the accident. In your example, we cannot say if the civil liability would fall on the bus insurance any more than we could now. I would have the opinion that presumed liability wouldn't make much difference in these types of cases.
Where it would make a difference is where an insurance company decides to put a case through the courts, especially in the case of a cyclist where they may not have insurance. I suspect that insurance companies may be less likely to "try their luck" through court (in the hope that the uninsured party is more likely to drop the case with less resources on their side) and would probably be more motivated to reach an agreement, unless the insurance companies think the nature of the accident genuinely shows the cyclist at fault. I can only think this is good.
But, of course, whilst the Daily Mail rants on about presumed liability enabling cyclists to claim insurance money from "hapless" motorists by hurling themselves at their cars then it is unlikely any rational debate can be had.
And also "presumed" liability is a million miles from "strict" liability, but it suits the more hysterical press to conflate the two.