Honestly, if you compare a boxing manual from 1900 to one today, there is next to nothing between them. In fact some boxing manuals from that period are still in use.
But one big difference is the "jousting" or "spearing" jab, isn't it? And that single difference alone does make for a series of pretty different styles, however you feel about them on a case by case basis.
Any pre-1920's boxer would get absolutely schooled by their modern counterpart for the most part. In fact imo even champs from that era would be hard pressed to make a top 10 contender ranking in the modern era.
Impossible to prove either way of course, but I very much doubt it. On the flip side of the coin, how would a modern fighter do in a bareknuckle prize fight?
Well, the boxing manuals of the era describe a long jab, thrown from a lean, as a single punch. It's a handme down from the original relationship between fencing and boxing maybe, though that's a thought only. It's a "jousting" punch, based upon creating a false distance to get the punch over. It's quite unlike the modern jab, and what it is used for.
You are correct about the jab being originaly based on fencing technique, but I don't think that it was only used in this limited way in Corbetts time. There do seem to be fighters of the era who used it as their primary weapon, though I am basing this on written accounts.
Roy Jones Jr. Corbett wins split Dec Ezzard Charles. Corbett loses unanimous. Michael spinks. Corbett wins unanimous Dec David haye. Corbett loses by 10 round ko Billy conn. A draw Gene tunny. Corbett loses by unanimous. James toney. Corbett wins by hard fought unanimous. Patterson. Corbett down twice, Patterson down twice. Patterson by 11rouns ko. Bernard Hopkins. Corbett unanimous win. Foster. Corbett by seven round ko Qawi. Pulls off a shock split decision John Henry Lewis. Corbett by unanimous Dec
Really the jab as described and illustrated in the day is not that much different than the jab Ali employed. In terms of basic technique. The jab was described as to be thrown, landed and then almost simultaneously step away to avoid a counter. Very reminiscent of a fencing lead. Corbett was trained to fight long distance so a 12-15 round fight in his prime should be a walk in the park. Impossible to predict how he would do as the film footage of him is as silient film quality as it gets. He was rated highly and I am sure he was very difficult to hit cleanly. In his prime if he avoids a ko blow I would expect he wins many 12 and 15 round decisions over many great fighters.