Not quite, my friend.

As you know, I am a stickler for the maths.

Bullet weight is proportional, yes,

but velocity is 'squared' so it is not a direct relationship.

A little increase in mass = a little increase in energy

A little increase in velocity = a much bigger increase in energy.

Try it yourself- keeping velocity constant, if you double the bullet weight, you get double the energy. Directly proportional, like you said!

Try the inverse, if you keep mass constant, and double velocity, you get a BIG increase in energy. The change in energy is much greater than the change in velocity - this is not a direct relationship.