You make a strong point, but I would argue there's more subtlety than you acknowledge. At least there are other metaphors that might shed light on the idea of agency.
For one, there's the coach of a team sport. We don't say that the coach played the game, but we do credit them with being a vital part of the team's success or failure. These artists seem more like coaches than CEOs to me.
One big difference between artists and both CEOs and coaches is that the products of an artists are standalone, enduring (except for some new media works) pieces. And I think that difference makes artists and the analysis of a technician in the production of any piece a somewhat unique situation.
A coach is different because the players get one chance to play the game. Art can be redone as many times as you have the time and resources for. When doing that directing the iterations and making the final selection becomes the important thing. For example, take this piece from the GP:
How much credit Chihuly deserves varies wildly with how that piece was made. If he had merely said "Make me some yellow/orangish flowers" then he doesn't deserve much credit. If the ~40 flowers we see were the result of 1,000 attempts with him directing ("Make this one 1" bigger, this one less orange" etc.) then he deserves almost all the credit.
A common idiom on HN is that "ideas are cheap". The artist has the ideas, we often naively credit then with the implementation too; the implementation isn't 'the easy bit', it's an essential part of creating an artistic work.
Duchamp's fountain is a fine idea that continues to inspire newcomers to that age-old what-is-art question; but truly the material science and manufacturing process and craftsmanship that went in to that urinals design and production are a cause celebre - greater than Duchamp's idea by far IMO.
Now reflect on Warhol's prints; derivative instead of visual design rather than artefact production. But Warhol designed and created the works.
IMO: commissioning art doesn't make you the artist of a final work that required artistic and crafting input from others. Warhol is the artist of his self-made silk prints; Duchamp's input to Fountain is curating, or social commentary.
The same is true in architecture,"Wren's" St. Paul's Cathedral would be nothing without the skilled masons. There's a line there somewhere though -- I wouldn't include the sandwich makers, the steeplejacks, et al., A amongst the creators of that work, ...
(This all brings to mind Gaia Hypothesis.)
Ah, says the modern artist, but the art I create is the image/idea in your mind and the medium I use is other artists and craftsmen ...
For one, there's the coach of a team sport. We don't say that the coach played the game, but we do credit them with being a vital part of the team's success or failure. These artists seem more like coaches than CEOs to me.
One big difference between artists and both CEOs and coaches is that the products of an artists are standalone, enduring (except for some new media works) pieces. And I think that difference makes artists and the analysis of a technician in the production of any piece a somewhat unique situation.