> Scientists could/do define the risk profiles for different drugs
The scientific risk profiles I've read have alcohol right up there on the top of the ranking for hardest, most damaging drugs. Sometimes it's at #1, but it's always right there in the big 4 with cocaine, heroin, and meth.
"Not defined as a hard drug" is a policy choice, almost entirely because of cultural/historic reasons, as you point out. Prohibition didn't work for alcohol, and it's not working for other drugs.
DUIs, on the other hand... harsh prosecution of DUIs is fine because they're crimes with victims, where other people are put into serious and immediate danger. That's a better approach than the overly broad, costly, and ineffective policy of simply incarcerating everyone for drug use.