Why not? If one guy hangs it up over the top a bit longer than the other, or on the low end one guy pulls a little more G as he brings it back around, it is most certainly going to change the dynamics enough over time to push one plane in front of the other. It has too!
You're right Fugitive, but without getting him to look at some films, I don't think he'll get it. I think he's fixating on the idea that the loops will (er, could)appear to be "egg-shaped" if seen from the front or back of the barrel roll "tube", and that's why he can't imagine the plane flying through the bottom being able to "gain" on the other.
Of course, "gaining" isn't the goal of the rolling scissors, so he's a bit off the mark right there... He thinks he's losing because the other guy can gain on him?
He's also apparently not "seeing" all the variations that occur in a given scissors, that give one pilot the edge over the other, even in similar planes, with similar E, and similar goals. Things that immediately spring to mind that can alter what he thinks he's seeing are misjudging someone elses E, someone "hanging" or "loitering" at the top, someone doing a simple roll at the top (without the elevator to make it a barrel roll), and the fact that one plane may be nearer to corner velocity, yielding a better turn rate, while one is slower, with a better turn radius.
And again, the fact he'd complain about someone gaining/closing on another in this maneuver is a telling complaint... If you're trying to close on your opponent in the rolling scissors, you're looking to get shot.
He's read enough to know how the maneuver is "supposed" to work, but when he doesn't see that result he immediately figure's it's the flight model being porked... It couldn't possibly be the pilot, since he can't be doing the maneuver wrong (or just less-good), right? For some, it's too hard to blame yourself for your own failures.
The real shame of it is that it's so easy to fix these problems. A little work with films, maybe some work in the TA, and "poof" the fights get easier, satisfying, and less frustrating.
You can lead a horse to water...