Well, the quotes rather give the impression that using magic needs intense concentration but there is almost none about magic not needing one. Its the impression that is important. Might have been made clear from the onset.
Jenn and the man situation is also curious. Why would Jenn need to make the spell last longer? I thought the spell was to move the roots and make them bind the enemy. But after that there should be no need for further magic. Roots are quite strong materials by themselves. A man bound in roots is very unlikely to escape. I was also a bit surprised when Jehanna admonished Jenn about leaving the prisoner because what Jenn did is more than enough.
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As for craft, I don’t see how magic reduces the mental effort. Craft requires great focus by themselves, magic also requires mental effort, combine the two and you might as well double the required mental energy. I’m not saying that it makes it impossible, I just say that in general not just the glass table (which is quite a feat) magic in production isn’t really that much of an improvement. Yes they can make better products but that doesn’t mean that the products made by magic is cheaper (incredibly cheap!) than ones made by hand. For all business sense, objects made by magic should have been more expensive, the law of supply and demand and all, not to mention the effort to make them.
“A driver of a car does not have to worry about making sure the pistons are turning, or that gas is flowing into them, or any of the other details of what makes the car go. Same for flying carpets.”
You are really set on the car analogy. A car standing still is very different from a carpet hovering in place. Turn the car off and it would stay in place, not so with carpets.
It may seem easy but hovering in place is quite difficult. Birds can’t even do that where flying is their specialty. Don’t expect that from modern air vehicles (hovering airplanes?). Hellicopters would wobble around when it hovers. The most perfect hovering that I could see with modern crafts are the tiny helicopter robots in many science channels. But then they require lot of processing power and quite sterile surroundings to do so.
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Thaumaturgy. There is some information in the special pages and with the small info there, Thaumaturgy is quite an impressive magic.
You might also confuse payment from profits. For example, matches are quite cheap but millions of it is consumed every day, so even with small profits per match, the huge number consumed would result to very big profits. On the other end, airplanes gives quite large margin of profits, but then the demand for them isn’t really as big, just thousands a year. So, in business sense, even if Thaumaturgy is somewhat lowkey compared to others that shouldn’t be a barrier against big profits.
As for the nobles, they aren’t the only ones who have the money. Even if other people have less wealth than the nobles, their sheer number is more than enough to compensate. That is why in products, like books, how many is sold matters a lot. Authors and publishers would love to make and sell a best selling book. More sold, more profits.
Also even if Thaumaturgy is rather dull compared to other field of magic and is relatively less valued compared to others, that doesn’t mean it has little value. Relative, absolute there is a difference. This coupled with the fact that magic wielders are rare and most it seems doesn’t choose Thaumaturgy. High demand and little supply, and by the law of supply and demand that makes for quite a profitable venture.
I think you should also clear up about the business side of magic wielders if this is going to be important in your book.