I think what perhaps confuses the short price brigade punter ['the only way to possibly win'] is the odds on offer and true odds. Odds on offer can never be more than a very rough guess, regardless if they are worked out mechanically on a computer, handicapped or the final SP by the public as closest to true odds.

True odds can only be worked out after a race by placings and beaten margins. Regardless of what happens during the race or at the start gate, the final result is the truth of the matter regarding true odds and what really was 'overs' and what was in fact, way 'unders'.

Approximately 70% of favourites lose, so that's a 2/1 chance of winning. A genuine negative expectation game chasing the shorties and regardless of how good the handicapping, the odds of getting it wrong and our money being on the wrong horse too often are quite large. Due mainly I think to what can happen in a race from the gates to the finish post.
True odds can go from odds-on to 100/1 in the blink of an eye and in less than a horse length, anywhere during a race for a multitude of reasons.

Maybe it is with this in mind, some successful punters see that 'overs' on the shorties are rarer than we like to believe and are looking very closely at the 3rd. or 4th.. to maybe the 7th favourites for more chance of genuine 'overs' among the prices those runners enjoy in a race.
Not betting them Willy nilly, but finding a few a week that have good things going for them that will be [hopefully] missed by the public and entering the starting gate with far better odds available that it deserves. If it's not missed by the public it becomes a no bet.

It might be along these lines of thought that some punters discover that the $7+ runners aren't so 'impossible' to win on after all. Very good handicapping skill and plenty of time and effort would be required of course, but I think the potential for good profits are certainly there. It's maybe all about true odds and perceived odds and boy, the public gets them wrong a lot and so do the bookies.