On a basic level, randomly beating up 4 people in the street, including stamping on at least one persons head by all accounts, is a serious offence.

The person on whose head he stamped could have died, particularly if they had a number of relatively common health conditions.

There is a legal rule (established in UK law which would I think be precedent here) in Smith v Leech Brain & Co (1962) if my memory of my law lectures 26 years ago is correct, called the 'Eggshell thin skull rule' in which it was held that a person was liable for the consequences of their actions if they were foreseeable and that arguing that the person was unusually susceptible due to their medical conditions was not a defence. (it's not restricted to head injuries despite the name - the original case dealt with molten metal causing cancer or something I think)

Normally applied to tort law (such as negligence) rather than criminal law but it seems reasonable that it ought to apply in both as I cannot see how it could apply in one and not the other.

Thus if the person whose head was stamped on were to die by some means connected to the stamping, he could be charged with manslaughter.

It seems to me therefore that an assault of sufficient severity to kill (even if it did not and even if that was not the intention) should at least result in some sort of custodial sentence and more reparation than a mere $5,000. 

It is to be hoped that a review of the case will arrive at a more appropriate conclusion.

I find it laughable that as a nation we can go on and on about violence being bad, wearing pretty ribbons and donating money, running expensive TV ads and so on and yet when someone indulges in outright thuggery on the street the result is punishment more appropriate for shoplifting.....!