If you want to do a comparison where the results are not definitively known in advance compare a 38 +P load vs a regular 9MM load.
158 grain @ 950 FPS vs 124 grain @ 1100 FPS is much closer than 9mm vs .357.
I don't disagree, except when it comes to some of the older .38 JHP bullet designs which seemed to clog and exhibit erratic, if any, expansion even when fired out of 4" service revolvers. Of course, the older 115gr 9mm JHP's could sometimes suffer from similar issues. We have some better JHP designs from which to choose nowadays.
I've seen the results of a similar comparison done in hosted gel testing, usually comparing a 125gr-135gr +P .38, fired from a snub, to 147gr or 124gr +P 127gr +P+ 9mm, fired from a duty pistol. (In one of the earlier tests the 147gr and 127gr +P+ loads were checked in a 4LD test, fired from a 3" CS9, too.) The newer snub loads seemed to offer a little less penetration than the 9 loads, although in one of them the 130gr +P performed (that day), fired from a 642, pretty similarly to a 127gr +P+, fired from a duty 9, in the Auto Glass/gel test. Probably toss a coin for any other day, or other shots, though.
The days of the 158gr LSWCHP/LHP +P have been somewhat eclipsed by some of the lighter .38 bullet weights of more modern manufacture. (I still have some remaining boxes of both the Rem Express and W-W SPD loads, though. I just seldom carry them anymore.)