Technically, it is very slightly cheaper by sand and silica. But rock and crushed rock and sand are commodities that are largely going to landfill, and I think this should be the case for almost any choice of crafting chains.

Okay, I had to look pretty deeply into this, it is highly dependent on what modules you are using. At +14% it would very nearly break even with the basic recipe for limestone use. Above this it would be worse. While also requiring two additional resources which push the total cost higher.

I am assuming it is meant to be a superior recipe, but if it just meant to be another option, trading rock for limestone, rare metals and pyroflux, and the cost of importing imersite, then it starts off nearly balanced but rather pointless before becoming totally inferior with higher productivity.

Limestone is the thing which really needs fixing but this could still use a buff.

I don't know where you get your numbers from but with tier 3 prod modules I see a very significant difference for everything. Like less than half the limestone. Apart from the balancing the second recipe doesn't really make sense. The icon indicates it uses Pyroflux but it's not an ingredient. Instead the recipe is very different from the original and Imersite is included instead. I thought about removing the recipe.