While the .357 Magnum is markedly more powerful than the 9mm in 4" barrel duty guns, the gap narrows somewhat in the subcompacts since the .357 Magnum cartridge loses markedly more velocity in a shorter barrel than the 9mm Luger. I've seen a 2" Colt Magnum Carry go down as low as 1220 foot-seconds with 125 grain .357 from an ammo lot that was hitting 1400 fps out of a 4" service revolver. A 115 grain 9mm that was doing 1250 out of a 4" will be down in the 1100s with a 3" auto. So, the .357 will still be more powerful, but by a somewhat lesser margin.
The difference will really be found more in design. The shape of the small revolver makes it faster to draw from a pocket than the squarer auto pistol. In the dusty environment of an ankle holster, many small autos build up enough crud to make jams more likely within a few shots, but revolvers tolerate that better as a rule. Of course, the 3" 9mm auto will "kick" distinctly less and will carry more rounds and will be faster to reload.
Hoping this is of help,