Here is some interesting data from firearmstactical.com:
Walther PPK/S (CCI/Speer JHP, 88 gr): 914 fps/11.55inches penetration/0.46inches expansion
Sig P226 (Federal JHP +P+, 115 gr): 1237fps/11.25inches penetration/0.53inches expansion
Yeah, I picked the data to favor my argument
But, I still think the point is valid. There are several 380 ammo brands that put out over 1,050 fps, 220+ fpe, and good penetration/expansion.
In general, 9mm JHP penetrates 10-13 inches and expands to 0.52-0.67. In general, 380 JHP penetrates 8-12 inches and expands 0.5-0.6. Performance is VERY close and obviously depends on length of barrel, specific handgun, and specific ammo. Consider that the P232 has a 3.6" barrel, and the MK9 has a 3.0" barrel. Which gun will have the better performance? I haven't seen the data, but I would bet the difference is closer than you think - that 20% additional length can go a "long" way (pun intended). 20% shorter length in short barrels = 10-15% loss in performance!
My point is that with good ammo, the P232 is no slouch...