You're right; drug addiction should indeed be treated as a health issue rather than a criminal one. However, his sentence was for possessing a significant amount of methamphetamine (Class A) and drug paraphernalia.
I know people who received similar sentences for having only a few ounces of marijuana (Class C) for personal use along with a utensil, though this was some years ago.
I think it's best not to say it should be a longer sentence because it's similar to a marijuana one, and rather ask why we prosecute marijuana at all (I know the answer is the referendum, but it's still dumb).
I agree, I voted yes to legalize and believe it should be legalized. It wasn't the best comparison just the the first thing I thought of related to sentences for abuse of the drugs Act.