He was wrong.
The older I get the shorter my barrels tend to get. I used to be a confirmed long barrel guy but as I shot more and killed more stuff I realized that long barrels are a PITA and any performance gain from them is grossly exaggerated. My 7mm rem mag wears a 24" bartlein and if it were 22 5/8" it wouldn't bother me a bit.
I wouldn't call him wrong at all. He was speaking in generalities though. He was basically saying a 7mm started giving up too much with a shorter barrel and it wasn't worth shooting a short barrel 7RM vs a 270. That they wouldn't be enough difference in them to justify the added recoil and muzzle blast of the 7RM.
Here's a great case in point. Link below is to a Rifle Shooter article, where a guy actually cut the barrel off of a 7RM, 1 inch at a time and documented the results. They are interesting.
For test Load #1 he used factory Federal 7RM 150 gr SP ammo. By the time he got to 23" the 7RM 150 Gr bullet was only doing 2821 FPS. Federal states the velocity of their 270 Win 150 Gr SP ammo to be 2831 FPS. So..... In these tests a 23" 7RM barrel was really only running at 270 Win speeds.
I think, generally, it is considered a true assumption that a 7RM really doesn't start to shine and pay for itself until it gets to a 26" barrel. It is just handicapped some otherwise. So why handicap it? You are paying more money for brass, bullets, and powder, for not much gain at all.
Given the results below, I would never shoot a 7RM with a 22.5" barrel. That's just hurting your shoulder and wallet for nothing. My 7RM uses a 26" barrel and I wouldn't have it anyother way.
Link to the test and results:
https://rifleshooter.com/2015/04/7mm-remington-magnum-7-rem-mag-barrel-length-versus-velocity/