Over 90% of outer ear infection is caused by bacterial infection, with 10% being fungal (and then, those are more liekly in tropical environments). The risk of fungal infection in non-tropical environments is thus fairly low probability.
There has also been several (4 that I can find myself) studies done on using acidic drops as the only treatment for ear infections, all which has shown them non-effective to clear an infection. Alcohol can also irritate the skin further, increasing inflammation.
Ear infections are however complex since most of the studies are either done on children, commercial or military divers. The military protocol in the Netherlands is to start with an acidic solution and then if the inflammation get worse introduce steroids. If that doesn't clear it, then add a combination of antibiotics and steroids. Steroids has the problem of increasing risk to bacterial infection, but the combination of using antibiotics with the steroids reduces that risk. It is this combination that doctors use in post surgery.
The Dutch protocol seems like the optimal treatment protocol for now, but it assumes you got a doctor to monitor it. My guess is that regular doctors jumps to the last step with the assumption that it is bacterial infection in order to minimize the need for further visits. One study I read also mentioned that adherence to correct application of the drops was one of the most significant factor in outcomes, which might imply an other reason to go for the strongest treatment first.
One thing that favors alcohol however is that keeping the ear dry is extremely important in addressing outer ear infection and preventing bacteria from growing. The theory behind vinegar and alcohol does thus seem quite sound from a theory perspective, stopping the bacterial infection before it get a chance to grow.