Yes, the penetration of a solid bullet in flesh (or ballistic gel), it correlates more closely to momentum then to kinetic energy. Thing is, though, heavy and slow handgun bullets, even those which are pretty anemic (by modern standards) loads, will penetrate more then enough very easily. Increasing it doesn't have purpose.
Something like, by now, 100 year old 45 ACP or .45 Colt with ball ammo, will easily penetrate well over 20" of gel, firing 200-230 gr bullets at some leisurely 800-850 FPS. Now, sending a 0.45 caliber slug with more then enough penetration is going to still work, just like it has worked for a bit over a century before the advent of modern ammo and works to this day for those who mustn't use modern ammo (eg. every army out there).
In fact, if you don't want to or can't (military, civilians in some EU countries, etc) use expanding ammo, you might as well stop here, ignore various +P rounds, pick a SWC (revolver) or ball (semi-auto) in large caliber with a heavy and slow round, and if it comes to that, be pretty confident with what you have.
However, expanding ammo isn't just some passing fad, and it requires velocity to happen (the bullet will consume a significant part of it's own kinetic energy to deform), and here the light and fast shines, as long as sufficient penetration is there. This is why you see so many +P rounds nowadays; they actually do need the extra energy to expand and still penetrate sufficiently.
Is it common to use kilograms for bullet mass in Europe? I've never seen a box of 9mm ammo described as containing "0.00745187 kg" bullets (115 grain).
It is common to express it in grams, so we would say that this 9mm fires 7.5 gram bullets. You can just plug in the number in the equation and then divide the result by 1000 to get Joules. Isn't the metric system grand?