I don't think there is anyone here who can answer this definitively. In other words, I don't know why one takes two Essences of Sight and the other four. It's possible they were supposed to be the same. It could be that both were supposed to need 4 instead of 2. It could be that the quantities were supposed to be reversed (i.e. longbow needing 4 Essences, shortbow needing 2). It's also just as possible it was done that way for recipe balancing reasons.
I know this is not a helpful answer, but it's the only one we have at the moment.
I'll move this over to the Bug Reports forum, so that it won't get completely lost and will get the proper sort of attention...if nothing else but to evaluate the recipes and the items to see if some vairance between them is legitimately justified.