I disagree, i think that is a perfectly fair sentence.
8 months is nothing, and he'll be out in 4, or less. The danger of this individual is his complete lack of judgement, and the 'premeditated' nature of what he did.
The difference with violent crimes being referred to, in my opinion, is that these are all subjective. They can be instant, emotionally charged reactions, where alcohol is often involved, which i think can go some way to explaining the leniency. Compare that against a premeditated attack on someone and the sentence will undoubtedly be longer.