I agree it's an issue. The difference in penalties may be too great in many instances. There are of course a couple of reasons sentences are, and should be, different.
Keeping closest to the viewpoint you brought up, many things are dangerous. Heck, MOST things involve some risk. Consequences should fit the actual risk. Suppose I shoot off some fireworks in the middle of some soccer fields, full of short green, moist grass (which doesn't burn). Another person shoots off fireworks in their apartment complex. We've both committed the offense of shooting off fireworks within city limits. One of us was a much greater danger than the other. One method of measuring the actual danger posed is that my action did not in fact burn even a blade of grass, his action burned down an apartment building - with people in it. You can tell that his action truly could have killed people if it truly did kill people. Since my action actually did no harm, probably it wasn't really that dangerous.
If my brother has two or three drinks, you probably would never know it by having a conversation with him. Yet, his BAC is probably over 0.08%. My wife is the opposite. Three drinks and she'd probably wreck before she got out of the parking lot. The blood test doesn't measure the risk. What DOES demonstrate the degree of actual danger is if my wife actually plows through a crowd of people. Both drove over the limit - one drove without so much as running a red light, the other ran into people. Clearly, one is more of a danger to society than the other.
You mentioned murder vs attempted murder specifically. Buying a butcher knife with the intent to use it on someone is attempted murder (one can argue whether it *should* be, but it is). Someone who does that is a danger to society. Someone who actually stabs people to death, successfully, is clearly a greater danger.
Secondly, crime and punishment isn't all about the criminal, it's also about the victims (or potential victims). If somebody got plastered and ran over your child, after having been warned about the danger via a previous DWI charge, you'd probably want to kill the motherfucker who ran over your kid. As a society, we don't want parents, spouses, etc acting as judge, jury, and executioner, taking vengeance on the criminal - so we offer a better way. Victims can (hopefully) see justice done without taking justice into their own hands. If someone drives drunk and does *not* hurt anyone, you probably don't have the same urge to kill the motherfucker - society can see justice done with a lighter sentence if noone is harmed.
You might say "we shouldn't want justice, you shouldn't want to kill the motherfucker who ran over your kid." Perhaps so, perhaps not, but it's how we are. We can't "should" that away.