You're right, but it goes beyond that.
We deal with a momentum formula we call "power factor" in shooting all time, the only objective way to make sure everyone has a level playing field and is dealing with the same amount of recoil.
The thing is, you can make the same PF shooting a light bullet faster, or a heavier bullet slower.
The same applies to a break cue, as your engineer friend implied. I have actually worked out the numbers, but something like let's say you can stroke a 23 ounce cue to a 25mph tip speed, and an 18 ounce cue to 28, they may actually impart the same energy to the cue ball, with the same results.
Bottom line is, go with the weight YOU like. What works for me, or anyone, may not be the right set up for you.