Something I've thought about for a long time now is how shitty a good majority of crafted curios are since a majority of them are objectively worse than the items that go into making them. Something I think that would work to get around this, while still having some RNG/shittiness thrown in there, would be to change it so that it follows a formula using the parts put into it. Something like the end product of the combination of items will have an LP equal to a range of 50% to 150% of the total LP from the items used to craft it. Each time you craft one, it will roll the dice and spit out product that may be better or worse than the parts used.
As for the mental weight and the Time needed to fully learn the curio, that can be left static. Or if the devs want they can make some form of RNG forumla for it that they feel comfortable with.
Overall my wish is for a vast majority of the useless recipes in the game to actually have a use instead of just being a "build this once to get discovery bonus then never touch it again" recipe.