I don't think anyone assumes what the tip their arrow with will result in a lost deer because when people let an arrow fly they expect the POI to be right behind the shoulder.

That is the problem as I see it, if you make a marginal shot you run the risk of losing the deer, fixed blade or mechanical. A fixed blade will get more of the arrow through the deer on a poor shot (all things being equal) but you still run the risk of losing that deer.

I made a marginal shot on a deer with the Rage 2 blade. I recovered that deer but I didn't like the results after going through everything over and over so I went back to fixed blades.

A bad shot, regardless of the head is a bad shot. I think this is where the focus needs to be.

Finally, look at it a different way, some guys who use mechanicals feel they have an edge because they fly just like their field tips. If they are drilling the target with their field tips they will walk into the woods confident that their POI will be where the pin is set when the arrow flies.

I had to overcome this mental issue when I first started because I was not confident tuning my bow to get fixed blades hitting where my field points did. Not saying everyone shoots mechanicals for that reason, but I suspect there are a lot of hunters who just shoot during deer season and a mechanical will give these hunters more confidence than a fixed blade since their practice time is limited.