I get where WHBS was coming from, even if he drank a bit of the Crosman kool-aid.

In the 50s, the new US market for airguns that weren’t BB guns was for home/garden use for (a) training juniors before moving on to RF/CF/shotgun or (b) marksmanship practice for “real” gun owners when they could not get to a range. The CO2 gun, handling and working more like a bolt action cartridge firearm, was desirable in that context.

In addition, and in particular, as WHBS says, the US guns, pump or CO2, were much cheaper.

My oldest comparative reference on pricing is the 1972 Airgun Digest. Your typical Benjamin, Crosman, Daisy, Sheridan “adult” rifles range from $44 (Crosman 766) to $66 (Sheridan Silver Streak). The European imports range from $79 (Webley Hawk) through $99 (HW35), $139 for an FWB Sport from Beeman, and an astonishing $478.50 (inflation corrected for 2019: $2900!) for the ARH custom 120-X FWB.

I suspect the price differential was greater in the 50s.

So his opinion, in the context of the US at the time, had great merit. British shooters were more into farmyard pest control or bell target, Germans, 10M match. Which led to different choices.