How can a dwarf produce a workshop that seems to have many tools in it from just one peace of material. It doesnt make any logical or practical sense.
A quick-fix for that, without completely overhauling the current system, would be to require more items for making the workshop, and for the dwarf to require tools to use it.
E.g. a butchery would require a table (instead or as well as the stone/block), and a butcher would require a meat cleaver or such like.
Or a forge would require an anvil, a bellows, a furnace (possibly just a rock/block to represent that), and a bucket for quenching, and the smith would require a hammer.
Also, workshops in the current state of the game provide no difficulty what so ever. They can all be build from almost any of the accessible items and they are an instant jump-start to any industry, thus making them a bit unfair.
I don't see how it is "unfair" that you can easily build a workshop. If you want a bit more work, the "extra components" described above would do that. But I don't see the point in introducing "fake difficulty" just to make it harder to start an industry.
Over all, I'm not really sure how much benefit this idea would have. The only obvious ones I can think of are:
a) It could make micromanaging worker skill levels easier.
Because at the moment, if you have several forges set for low-skilled smiths, and several set for high-skilled smiths, then it can be a bind assigning jobs to each forge separately. Whereas with this system, you could have one workshop area with six forges, set that to low-skilled dwarves, and set the whole area on "copper caps, repeat". And then set up a separate master smithy with three anvils, set to high-level skill, and assign all your steel and gold jobs to that one.
b)
If dwarves need to use tools in their work, it will make storing the tools easier.