Well your primary craft skill should be 100% efficient as it is now
Your secondary and third craft ability somewhat in the range of 30% - 50% in production.
In real life, you dont make all the things you got right now, yourself
That computer u using, someone else made it, the car you drive, someone else made it. lol. I think u got my point
I totally disagree. Im a builder in RL, and I am very capable of doing more than one thing. I can lay bricks, do carpentry, plumbing, concreting, tiling, paving, landscaping, administration. And while I can do all this, I am still quite capable of doing other things, like cooking, I actually made this computer myself, though of course I didnt actually make the components, but we dont make any of the components in game ourselves either :P. I can weave and make cane baskets and stuff (my dad used to own a cane shop), I can fish, I can find things laying around, and Im really good at digging dirt.
If I were able to make a makeshift sword, Im sure I'd be very capable of making tools also. Its totally ridiculous to say that just cos you're good at one thing, you cant be good at another thing. It is far too restricting gameplay wise, and people will get the shits not being able to do more than 1 thing. In sandbox games we should be capable of learning as many skills as we like, though of course add snowballing difficulty to it, so it does restrict it to a degree.