Steel bows, although uncommon, actually can be found in and around India.
But, exceptional. If steel was superior we would know of english longbows made out of it.
Or the English metalurgy was not up to snuff. Or the fact that yew was just cheaper and more convenient than steel. Or the idea of it was unknown in distant Europe and the idea of making bows out of steel just wasn't an innovation they had made-heck, England was a bit unusual with their insistence on using bows instead of crossbows after the rest of Europe started transitioning.
It proves that Steel bows are possible with the right metallurgical knowhow. Note that the Indians did not themselves use crossbows-steel bows already filled the niche that crossbows and longbows fulfilled in Europe, complete with their own dedicated armor-piercing projectiles, much like those weapons.
The historical record is pretty clear on this in regards to the relative power and range of crossbows:
Worst Better Best
Wooden Crossbows------->Composite Crossbows-------->Metal(steel) Crossbows
Given, that corrects my opening statement which could have more completely been: "Historically composite crossbows are a bit more powerful than iron (for a given draw effort)"
You seem to have come round to accepting the premise of my point here - that woodcrafting technology can make more effort-efficient prods than metalsmithing: "They need to have higher draw weights than their bow counterparts to achieve the same results". With even more powerful prods an extra crank on the loading mechanism is a price worth paying to get to higher overall power level.
Please don't. You have pivoted on your position several times already, sometimes even within the same post. Your original statement was that they were more powerful than iron or wood, and that crossbows of that were not composite should be less powerful/treated as having lower quality.
And yes, that extra draw weights they could handle did historically justify the slower rate of fire of crossbows and the lower comparative energy transfer efficiency to the projectile. But you only really start seeing those benefits with much higher draw weights-higher than you can get by using 'gorilla strength' to pull back the string. So efficiency differences between the materials is secondary to the draw weight of the bow-if energy transfer efficiency was your concern, you'd be using a bow, not a crossbow. Though I am dubious that there is a huge efficiency gap in energy transfer between composite and steel, considering you claimed that this was due to the 'release/firing mechanism' (the nut) which would be entirely unrelated to the efficiency of the actual crossbow limbs which you seem to have extended this claim to.
Single piece wooden bows/prods can also be effectively composites by having two different growth types of wooden running through the length.
So at least a rough logic exists for enabling bowyers to make slightly more powerful dwarf hand drawn crossbows out of multiple crafting materials including wood and bone. 'Composite' would not be a terribly innacurate label for such technology.
Yes, theoretically yew would make a better material for crossbow limbs than (for example) pine.
It would make sense for dwarves to make crossbows using horn to make composite crossbows, and it would make sense for those crossbows to be better than ones with purely wood limbs. That does not mean that they should be better than steel crossbows.