Traxx, yes it's just as lethal. From my experience you get less string torque on release, so you have to learn to compensate. After that, it's no different from any other release and can be used on any bow. I don't tend to use it on centershot bows because of torque compensation (something that just takes practice to deal with, but as I don't own a centershot bow I can't practice it) but there's nothing that would prevent you from doing so.
As to the lethality against the Spaniards, let me talk for a minute about Pop's bow. He had a bow that was either captured during the Seminole War or more likely was made by a refugee that came south with the Red Sticks. It was (as I remember) about 68" ntn, made of bald cypress with a sinew backing. It was scalloped on both sides with the traditional diamond nocks of the Southeastern tribes. It had a gut string and was covered with what looked like thin deer rawhide. Traditional "Cherokee" D bow profile, bend through the handle. Catfish skin handle. I think that was added later.
That bow must have drawn 80-90#, based on how hard it was to draw against my at the time 70-75# draw. It did that at the chest draw, at full draw it certainly was heavier. That's plenty sufficient to punch through Spanish armor, never mind if you hit an unarmored area, which they were more than skilled enough to do. I used to shoot at the 80-90# mark and I could get near full penetration on a cinder block. That's not advised, of course. It could shoot through a car door up to the fletching. I can no longer do that, but the things I wrecked shooting straight through my styrofoam block targets caused me to think long and hard about how strong they were in battle. Add to that that the cane arrows would often shatter on impact and you have a recipe for festering wounds. At those weights the horses weren't safe either.
Many arrows had fire-hardened wood heads. Those were strong enough to pierce the plate armor, and the shaft breaking afterwards would have left the head in place. Flint or obsidian would shatter, causing a multitude of cuts and bone would stay in the wound like wood. (I know I owe everyone a bone arrowhead how-to, but I'm just now getting to be active outside again.)
People underestimate the power of bows routinely. I've seen a 25 pound bow get a double passthrough on a deer with good shot placement and shaving sharp head. To put things in context, on TradGang a person posted an elephant hunt they had been on. A 90# trad bow was enough to pass through and break a rib on the opposite side, which was lethal to the elephant. The Ashby report also shows what arrows can do against a multitude of very large game mammals. 60# has been enough with the proper head choice to kill an alligator by entering the brain cavity.
The grip is not what kills, it is the shot placement. In that Natives excelled. They lived as I did with the bow, but I had to go to school and they didn't. If I had grown up like them, maybe I would have been as good as Pop. But as to whether they took out the Spaniards like they said they did, I believe it's completely possible.
Makes me want to go look at the cypress boards in Flomaton.
