Don't set yourself up.
Reminds me of the time you told me you could make a graph with one axis.
Whether a skid plate stiffens the frame in any measurable/detectable way depends not only on its own construction, but also on how and to where it mounts onto the frame. They rarely bolt onto things that are "that" stiff, or use bolts that have a whole lot of clamping force. If you stick the tail end of one in a vise and grab the top front, most skid plates will turn out to be pretty flexible, anyway.
This times 123 scamillion. My Motion Pro glide plate attachment is in no way solid enough to do anything negative. And that photo is so very relevant to Krannie. Again.