Vin Mariani was 7+mg/oz with a relatively low alcohol content which would have been further mitigated by the stimulant effect of the cocaine in any case. And then of course other concotions (including Coca-Cola) had no alcohol at all - Vin Mariani is just a fun example because of the endless famous names attached to it.

Obviously you're right that the absorption is going to be different and a modern coke head with high tolerance likely wouldn't even notice it had anything in it. But give it to a normal person, and they're indeed going to be coked out - in very much the same way that small doses of adderall to non-users can have a very significant effect. The obvious example there being college kids buying pills around around finals.