Your discussion of the first moral luck justification

Identical behaviour is hard to judge

underplays the informational value of the actual results of the behavior. In the case of the drunk drivers, here are a few factors that influence the dangerousness of Alice and Yelena:

• how often they drive drunk
• how adapted their nervous systems are to a given blood alcohol level
• how fast they drive
• whether they drive on crowded roads or at high-traffic times

I'm sure you can think of many others. The parties involved have every incentive to hide any unfavorable evidence relating to any of these. But one fact that the legal system usually does have available is whether an injury actually occurred. Moreover, unlike the factors I listed, we know the exact magnitude of the relationship between injury and the result we care about, because that is the result we care about.