I wonder if the decreased terminal performance of expandable broadheads will be evened out from increased accuracy by the guys shooting out of tune bows and under spined arrows that spray fixed broadheads everywhere.
Oregon changed its laws to allow mechanical broadheads a few years ago, and I did some of the research for us that lead to this decision. rclouse79's point was a main theme in my research.
I see many out of tune setups at our public ranges in the weeks leading up to bow season. I believe that poor shot placement is a much bigger concern than the likelihood of mechanical broadhead failure. So, if mechanicals can improve shot placement by creating less front-end drag on the arrow, that's a win in my book.
The classic study on fixed vs. mechs over time was done at the
Naval Support Facility Indian Head. Yes, just deer, but we see that even back then mechs were not showing some abysmal failure rate. Obviously, you need to shoot enough KE to get the mechs to work well, especially on elk.
Dynamic arrow flight is another thing to consider and doesn't the attention it should. It seems many guys are focused on shooting micro diameter arrows with high FOC, which some of the latest Firenock podcasts claim are not optimal for high speed compound bows shooting carbon arrows. Dorge claims that micro diameter arrows are losing energy more downrange energy than a standard .246 arrow because the micros have thicker walls and take longer to "recover". As a result, these super skinny arrows are not entering the animal as straight as they could at typical bow ranges (20 -30 yards) and perhaps bending on impact more than a standard arrow. By contrast, a standard diameter arrow tends to recover by 18 yards and will enter the animal straight and stay straighter -- thus more penetration and better broadhead performance.
Splitting hairs here it seems, but I wonder if inefficient arrow flight and flex could influence so-called mechanical broadhead failures. If an arrow hits at an oblique angle, the broadhead isn't going to work as well no matter if you shoot mechs or fixed.