Likening him to a composer directing his own symphony makes a lot more sense- no one would argue that Mozart wasn't a great artist just because he couldn't play the whole symphony by himself.
A better question to ask is, "If the composer merely told others what to write, is it actually the composer's music?" This is an unbelievably common practice, and IMO, the answer to the question is no.
To me it's like an artist provides a detailed plan of how to build a monument, and then certified builders actually construct it.
Of course if an artist just gives a few rough sketches, and then a civil engineer provides the detailed drawings, and the builders construct the monument by them, then the artist is a co-author at best.
I don't know how specific D. Chihuly was in his instructions. I just think that such a separation of labor is possible, when the artist does the artistic stuff, and a performer follows on with the technical execution. In an extreme case, a machine (such as a music box) can play Bach, but that machine can't play without Bach having written the notes.
The generally accepted answer is "yes, this is composer's art". But it's also generally accepted that those who render the piece also take part in the art, in a different way. The bigger the influence, the more noticeable part it is. You don't normally ask who plays particular violins in an orchestra string group, but you do notice the first violin, and the director; you say "Gould plays Bach", or you say "Band N covers band M's hit". The influence of the performer is very visible, and makes a lot of difference. Still, without the composer's art, their performance would not be possible.
I don't see why this parallel can't apply to other collectively performed art (or any activity).