At close ranges and not in high winds, I'm just going to say that a good fixed blade head is always better.
You cannot say you will never hit the shoulder blade. Anyone that says "just don't hit the shoulder" is being narcissistic and using specious reasoning. My 2 biggest bucks (one over 140" gross and huge body), I regrettably drilled the shoulder. I didn't get full penetration but my QAD Exodus got into the vitals just enough (about halfway) to put them down within 100 yards. My setup for those two bucks was a slow Bowtech Revolt 60 lbs 30 inches that shot a 420 grain arrow at around 263 fps.
I seriously doubt a mechnical would have done that and would have just left a broadhead heavily jammed up in the bone and a crippled deer.
2 things are driving mechanical sales, I think. First, a lot of average archers can't get fixed blade heads to fly, so they go to mechanicals. Second, people now have this obsession of gory blood trails and watching the deer fall within 10 yards. This was never an expectation of bowhunting until the last decade or so. Put a decent cut fixed blade through the vitals, walk to the last spot you saw the deer, and you'll soon find a nice blood trail right to the animal. It will just look like someone poured it out with a watering can and not a bucket. The increased bone penetration is worth giving up any advantage that mechanicals have.
A reason so many professional archers hunt with mechanicals (Bowmar, Bee, Morgan, etc) is because they want to shoot 60 yards and farther and often in windy conditions.