This is the way I see it, using animal bones for an example:
Obviously most land animals would have bones; therefore you should theoretically be able to get bones from any animal. However, your ability to retrieve the bones is what changes. When you start, you'll get bones, but they'll suck and be, idk, cracked/broken bones. You can still make a spear, but it will kind of suck because your bones are almost worthless. As you continue to invest time in harvesting bones from animals, you become more proficient and are able to more carefully harvest them, giving you a better bone to use for your spear, maybe making the blade longer or wider.
To keep people from just farming low level mobs for the bones, this would probably be countered by either:
A: A game mechanic requiring certain mob level or bone quality level for an item. It's intangible and wouldn't "make sense", but it would work for the game.
B: Make higher level spears require "better bones". The bones of wolf like species and the bones of a dinosaur species are, I'm guessing, a different density and are larger, which would give you more room to make a better spear. This is tangible in terms of "making sense", but would need to be thought out.
Now this is just for your quality of making bones; there would obviously be the crafting experience too that would increase; you are able to make a stronger spear by being able to better wrap the spear tip to the wood; or you're more proficient holding one, or whatever.
Power gamers exist already in large user-based MMORPGs and have a nice hold on the market in terms of AH, but people still like to do their own crafting I think. Maybe making some higher quality spears requires you to do it to your own specification, making it so that you hold it perfectly, so if someone else wanted to use it, it wouldn't work as well or they wouldn't be capable of using it because they're not proficient or something.