I know, it does fill an empty spot, a 9 mm magnum that can fit a shorter action and adds another round to magazine capacity, but an empty spot doesn't mean that it need something to fill it. not at all.
That’s just it. There isn’t even an empty spot. The 9x23 Win is squarely in the spot that the ROF is supposed to fill. It was designed to fit the 1911 package and provide higher performance than the 9mm Win Mag.
The guy who set out to design the 9x23 Winchester had a very similar idea—he wanted the capacity of a 9mm with major power factor (back then that was 175 which corresponds to a 125gr bullet at 1400fps) and a round that would fit into commonly sized pistols. He started with the 9mm Win Mag like the ROF designer did. His size constraints drove him to a COAL of about 1.3”—very similar to the ROF.
However, because he understood basic internal ballistics, he knew that shortening a case and then asking for more performance from it would result in higher pressure. Therefore he strengthened the case as part of his design process. So he ended up with a cartridge that would more or less duplicate 9mm Winchester Magnum ballistics in a 1911 sized cartridge—but that had to operate at about 10KPsi higher pressure to achieve that goal.
That means that anyone who wants a non-bottlenecked 9mm that will fit in a 1911 and more or less duplicate .357Mag performance is in luck. That cartridge already exists in the form of the 9x23 Winchester. They may also find some comfort in the fact that the case is specifically designed to handle the inevitably higher pressures required to provide the performance of the parent cartridge in a shorter case.
People who are interested in this topic would probably enjoy reading through the discussions about the ROF on TFL—they go back as far as 2015.
It may an instance where the statement is literally true but is still deceptive (probably unwittingly).
It is a possibility, but quite unlikely. Both because that kind of effect would be pretty minimal in a pistol length barrel, and because the load data provided in the article doesn't suggest anything unusual or proprietary about the propellant.
Of course, even if that turns out to be the case, it wouldn't actually mean that the ROF outperforms the parent cartridges, because with the same propellant the parent cartridge would still retain the advantage. It must because of the limitations of internal ballistics.