OK - you are mixing things a bit. I am sorry if I was not clear when I mentioned this only applies to the moment of impact. The algebriac expression as shown only captures fixed, snap shots in time. Notice there is no time component in KE=1/2mv^2. What you are alluding to is the acceleration (or more correctly in this example, deceleration - just switch the sign) dv/dt component - which involves differential calculus and a few more equations - and many more variables.
Expansion of the projectile is post impact - and that is where dv/dt comes into play. The greater the dv/dt (deceleration), the more energy is passed to the target - as they say, its not the fall that kills you, its the sudden stop - same idea.
So lets put it all together. KE=1/2mv^2 relates mass and velocity to kinetic energy at a given time point. Bullet expansion as as a result of deceleration - do we have an equation for that? **** yes we do. The grand daddy of them all: F=ma. OK, so what that really means (putting into calculus language) Force = mass x dv/dt. So, the larger the dv/dt - the more force is imparted on the object. How do we get more dv/dt from a bullet - make it a hallow point.
Again, I noted the KE equation is limited in what it tells us - it is this limitation that permits the debate to continue - that was the point I am trying to make.
I cant imagine a bullet that passes through a body with no change in velocity - Newton has taught us this is not possible thanks to conservation of momentum. Two objects can not impact one another without changing the vectors of the involved bodies.
Now, taking it all into account - what do we want to do in order to impart the max energy on the bad guy?
A fast moving bullet - I dont really care how heavy it is as long as its moving fast - that can slow down really fast once it impacts an object.
At impact: KE=1/2mv^2.
A few milliseconds after impact until the bullet stops: F=mdv/dt
Got that? That is not subject to debate.
What is, however - is some bullets are really fast. Some slow down really fast too. The holy grail is a bullet that does both. Hence gun shop post-docs like to debate which is better - all the while not realizing what we perceive as wound damage is the inter-relation of mass, velocity, acceleration and time. Its hard for folks to think in 4 dimensions at the same time - that's why Newton came up with calculus - when he was 20. We didnt even get into the densities of bone versus muscle versus sinew, nor the change in directional vectors that are also taking place, and heat, sound, friction etc.
I still assert - I don't want to get shot by any gun or caliber. Ever. Pretty sure they all hurt.