If the fight happened in any other era, Willard likely would have won. - Dempsey would not have been able to stand over him. - Willard would have more time to recover. - Willard would not be allowed to clinch as much in the current era, or as much - Dempsey would not be able to hold and hit -Willard was a slow starter. If he can last through round 1, and figure Dempsey out, I can see him stopping Dempsey in the later rounds with a nicely times right hand. - Iron Rod...... ............?
In the same way that his was. It is true that it took a long time for Williard to get into his fight against Johnson. It's no more outlandish than your theory.
There are certain things to offset these factors however. With the three knockdown rule, Jack might have had Willard out of there in the first round, even with the neutral corner rule in place. I cant see any modern reff letting Willard fight on with his eye socket smashed in like that, so the fight might well have ended sooner.