Ralph has written extensively about the MPF and how it translates to other clubs. To much information to get deep into in this forum, but a quick overview. Drivers – all of todays modern drivers are basically Ultra Game Improvement Drivers. Of course, different settings, etc. can influence how any particular modern driver will perform for any particular player, but if we measure all in a neutral position, because of the size of the todays drivers, very difficult to find a variance in cg location that is significant enough to make them play noticeably different. MOI’s are all high because of the size. So with drivers, it’s all about the fit. The “mass and dimensional characteristics” are all too similar to be able distinguish a clear enough difference to put them in different categories like irons. Fairway woods and hybrids are a lot like irons and it all depends on the cg location, MOI, etc.. Below is a link to a page that describes this in a basic way.
With regards to wedges, Ralph developed a way to measure playability based on multiple factors, including sole angle, bounce, leading edge height, leading edge grind, etc. Section 12 of his book tells all about it. Too much information to write here. Below is a wedge fitting chart we put together years ago to that explains, in part, the features of wedges and how they rank from a playability standpoint. I would highly encourage you to get the book and read that section if you want to know the facts about the playability of wedges.
Shafts playability is simply based on the shaft profiles and data we measure. It is not really based on shafts being forgiving or not forgiving, but based on features that match certain player and/or swing types based on a few simple criteria. Basically the MPF for shafts (the basic questions that result in the MPF code) eliminates shafts that should not be considered and gives a list of shafts that are in the ball park for consideration. Once that is done, up to the player and the fitter to dial in the shaft performance.
I would encourage you to get Ralphs book. It’s timeless, factual, and a great reference tool. The link to the book is below.