I think that's probably an over generalization.

For example, Federal's current .357 Magnum "promo" load with a 158 gr JSP average 1296 fps in my 4" revolver, and with an SD of only 9 fps. The bullet is not high tech, but the load offers good performance and accuracy, with a very high degree of consistency. Not bad for a promo load.

Winchester's 158 gr JHP self defense load in comparison generated an average velocity of 1225 fps with an SD 20 fps in the same 4" revolver.

The Federal's 1296 fps is every bit as hard as I can push a 158 gr XTP in a 4" revolver, and it's close to the 1340 fps that I regard as maximum in a 6" revolver using 15.5 gr of 2400.

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Now…some folks also might be confusing yesterday's .38 +P loads with yesterdays .38 Special +P+ loads. In the 1970's it was not always PC to shoot bad guys with a .357 magnum and many departments ordered .357 Magnum revolvers, but specified they be chambered in .38 Special. Ruger, for example, shipped a lot of Police Service Sixes to police departments chambered in .38 Special.

Many of these same departments and federal agencies however then loaded these ".38 Specials" with .38 +P+ rounds. They varied in pressure from 23,500 psi to 30,000 psi. At 30,000 psi a 125 gr or 158 gr +P+ load gave about 90% of the performance of a .357 Magnum.

The old Border Patrol load was no where near 30,000 psi but would still launch a 125 gr HP at 1,200 fps from a 4" revolver.

In comparison, a 20,000 psi .38 Special +P load will achieve 1050 fps from the same 4" revolver.

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There also may be some confusion with the pre-.357 Magnum .38-44 loads. These were intended for large N frame .38 Specials and it's essentially what led to the development of the longer .357 Magnum.

I have .38-44 load data that will send a 158 gr XTP downrange at 1250 fps out of a 6" barrel. That's for all intents and purposes .357 magnum performance compared with the Winchester example above, and it's only 50 fps off the pace for the Federal example.