They do, that’s correct. However, as you have stated, the Feds could still make an arrest. No law may contradict a federal law, period. States impose their own laws on many different issues, but that does not make them legal.State Marijuana laws contradict Federal laws. I know the Feds can crack down, but so far, of course, they have not. Laws Can be passed at state level. Whether they can stand up to a legal challenge is something else. State abortion laws come to mind; these are much more prevalent than pot laws.
The problems that face the Feds are 1. There’s not enough federal officials to make arrests, 2. There’s not enough fed lawyers to try all the cases that would need to be tried, 3. The laws that the states are making really have no victims other than the person involved. The list goes on.
How you would feel if a state passed a law that permitted robbing banks, or we’re allowed to murder our spouse’s lover, or we’re allowed to beat up a drunk if he’s being a nuisance? See how weird it can get if states would be allowed to write their own laws?