Here, Kofman uses false equivalency and misses the point completely. Here are few things he misses:
1. PAK-FA has an official title and is known as SU-57 and is in series production, with the contract for first 76 aircraft signed few days ago;
2. Being Low Observable while boasting outstanding classic and modern, cutting edge, combat capabilities and performance beyond "Stealth" feature, such as SU-57 has, and having a flying embarrassment, aka F-35, built around primarily LO in radio diapason is not the same. Evidently Kofman does not recognize this crucial difference;
3. Kofman also fails to recognize the fact that in any potential NATO (USA)-Russia conflict, US "Stealth" aircraft would fly against Russia's Air Defense not against American one and here the capability abyss separating the two can not be larger. Kofman, as a "military analyst" should know that;
4. I omit here what I write non-stop about: modern air-defense signal processing and sensor fusion removes most, grossly overstated to start with, advantages of LO in a EW and sensor dense environment of the military peer. In the end, it is known fact that depending on the conditions even SU-35's Irbis radar "sees" F-22 at the ranges of up to 90 kilometers;
5. Finally, it is not a good practice for analyst to defer to the potential enemy, such as Russia, in terms of what she is doing and use it for propaganda, or self-medicating (most likely), purposes. In the end Israeli Air Force still cannot coherently explain what kind of bird damaged IAF's F-35 in Syria, same as why IAF prefers to launch at Syria (allegedly Iranian) targets from the international airspace.
Moreover, ignoring a dramatic difference between the use of air power in Russia and the United States, especially projected against the background of radical doctrinal differences, is hardly a competent idea, unless, of course, it is used for entertainment of amateurs. But then again, for that--there is a rich and vibrant field of Clancyesque military "literature", where such theses, as Kofman advances, belong.