Light isn't an issue with them unless you really goof up.
Exactly. And exactly why I don't agree carte blanche with this statement:
It's where you hit not how much the arrow weighs!
My first 30 or so deer were pretty much all pass-throughs as well; then one day, I didn't hit as far back as I would have liked and squarely smacked a shoulder blade. I would have liked to have had a heavier arrow that day.