An example of why this exists: You have an item, lets say Shock Absorber. It is used in the final recipe Car Suspension and in the toy Pogo Stick. Pogo stick is a Rank 10 synth, and Car Suspension is a Rank 30 synth (used to make a Rank 35 Car). So what rank do you make the Shock Absorber. Rank 5, so it is below the rank of the pogo stick? Or rank 10? Those are both too low for the Car Suspension. Maybe Rank 20 so it just below the level of the Car Suspension, but not too low, but it still ends up being to high for the Pogo stick.
Compound the problem with the fact that there may not be many recipes because lots of them just didn't get finished. Maybe there is a Rank 50 High Tech Suspension for the level 80 Space Shuttle.
In this example, we have our pogo sticks (walking) but we KNOW we're getting cars (chocobos) and space shuttles (airships) and maybe (if we're lucky) we're going to get to trick them out as it were, but the recipes just aren't in the game yet because the items aren't in the game yet.
When you take that into account, it makes sense that some of the recipes are off. Now, the economic argument stands for things like cotton robe front being used for cotton robes - because you don't use cotton robe front for canvas robe. You make a canvas robe front.
I imagine SE envisioned people would grind on cotton robe fronts, then turn around and sell them so that people could grind on robes. Unfortunately, that didn't happen. At this point, they should (and have already said they would) fix the problem in those cases by making the cotton robe fronts lower level.
This works for SOME items. It doesn't take into account cross-class uses for items. An Ebony Super Wood plank might be used regularly throughout CRP for making Ebony shields, Ebony Surf Boards, and Ebony Tree Houses (all high level synths) but also be used in an Ebony Backboard for the low level synth Ebony Dart Board. So while the dart board is REALLY hard to make, even though its a Rank 1 item, they can't make ebony planks easy because there are a LOT of high level ebony things that would be TOO easy if ebony planks were easy.
And that's a breakdown of whats what, IMO.