In theory I woundn't dispute you too much. But it's noted that the impact is affected not only by some physics unit, also time and space interval, that's where your t comes from.After thinking about it, if it is impact, then momentum can be used and actually in most physics book, it is the only correct one to calculate the one deminstional inelastic collision. In that scenario. we have to consider impulse, J=F*t, the bullet travelling at a much faster speed would have a much less impact time. Thus the force acting on the tank armor would be:
One reasonable assumption would be since the bullet travelling 1000 times faster, the impact time would be a thousand times less than the coconut. Actually the bullet would probably have a much less impact time, because of its shape.
Then the large amount of F acting on rather small area, would have a even bigger pressure, and that is how do you have deformation.
The problem of momentum as the measurement is that, it may have something to do with the time(speed), but it's hard to express it in space.
But energy can, you can condense the energy both in time and space interval, exactly why people choose it.