The fact that resources are so limited - and acquisition of resources through trade is extremely difficult. I don't mind a huge chunk of stone being required to make a wall, or even a stone chair. But when a giant heap of marble produces only one stone earring, then the game's simplification has been taken too far.
It's too expensive, resource-wise, to train certain skills, but skills increase so rapidly that people can be come masters of their craft after less than a year.
I dislike losing access to resources because of lack of skill (example: mining), and I dislike that certain tasks are completed so quickly (most especially: mining).
Yes, there are basically two types of resources:
Infinite
Finite
Infinite resources are just going to accumulate over time. You always have ready source of raw materials. This means several things:
1) You can overproduce on grand scale You have infinite raw material at your disposal, and you can buy out whole caravans with them over and over again.
2) Since you have free material, you can train every single peasant to be legendary on them. This means that your skilled workers are quite easily replaceable.
You can have as many legendary weavers/dyers/threshers/clothiers as you want. Theese industrues work as perpetum mobile engine basically: no input, huge output.
This is especially pronounced when you can train your dwarf on items that are essentially having no quality but are quite usefull: Bonecarvers for example can obtain legendary by creating bone bolts (bone bolts being always usefull regardless of quality).
This of course contrasts with:
Finite resources. They will eventually run out and/or have rate of acquisition capped harshly. They, of course have some implications too:
1) You will run out of them eventually. There is little you can do to get more raw materials.
2) Training is expensive. Skilled laborer is irreplaceable.
For example: Smoothing. You will eventually run out of stone to smooth, and to engrave. If you loose engraver, you will have to smooth certain amount of tiles too get new one to state where you can give him skill-requiring job (engraving) - roughly two fully dug 2x2 zlevels.
This, as you can imagine, leads to problems if loose several engravers in succession. Eventually you run out of room to train in and it is game over - no more materpiece engravings for you, ever.
Mining works like this too: It is even harsher since most maps have very limited soil z-layers to train miners without destroying stone, when you are done with them, every lost miner means that you are going to loose ~100 stones as he trains.
Even if you can import, you are going to obtain materials much slower than your dwarves die of old age.
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If you would try clothesmaking industry you will see the other coin: You simply stop caring about resources and you are going to be annoyed by masterpiece spam from weaver/dyer/tailor.
Eventually, moment will come when you will simply stop caring and just stuff everything you can onto caravans to get rid of that damn stuff, having caravans leave with profits measured in hunderds of thousands.
Ballance is simply off.