i wish i was a scientist
I wish i had the scientific reasoning for this, and I used to think the same thing, same motion, same thing.
But, If I were to plug 200 lbs (my body weight) into the lat pull down machine I can hit out over ten, wait a couple minutes, hit out ten, wait and hit out maybe 8.
If i grab the chin up bar (tactical grip) I can go about 8 before my form starts to crap out. wait a couple of minutes and hit out about 6
I think that it is because of the swinging moments that u can't get urself into with the tactical chin up, with a lat pull down ur sitting down and rip the bar down with ur legs and lower back as well as the upper back, with a tactical chin up, its pretty much all back. You have that leg thing holding ur legs down, maybe that is where the difference is.
I wish I could find the quote by Pavel in Beyond Body Buidling but he says the same, cable pull downs are not an alternative for chin ups, as frequently the case, he doesn't explain why but he is right.
After doing tactical chin ups my back relaxed looks more beaslty than my back did when it was flexed while I was doing the lat pull downs, and now I'm doing tacticals with additional weight, good strenght with good size.
I wish I could explain myself better, I'm sorry I've made a bold statement without a reason, but you gotta give the tactical a try, it is definety one of the best back exercises there is!