Phantom, Mechanicals were designed to match field point performance. But your concerns are valid. Mechanicals were introduced shortly after carbon arrows became popular for hunting. Archers would purchase the new mechanicals, Punchcutters, because the carbon arrow was so light that tuning was next to impossible with a heavy draw weight. To cover this many started shooting the mecanicals. If you look on an arrow chart, you will see a recommended arrow spline for the weight and draw length you shoot. You can increase in size and tune your setup. But if you drop one or two arrows lighter, the spline is to weak and arrow flight is erratic. This is what happened with the superlite carbons. Stay with the fixed broadhead and eliminate one more thing to go wrong.
Good Hunting....