Would you consider these microsculptures works of art, or a craft?
Question for you: Would you consider photographs to be works of art, or a craft?
I think there is no serious disagreement that photographs can count as art, and these microsculptures were carefully planned and posed as art. If you are going to suggest that they may not clear the bar as art, then it seems to me that you would have to rule out photography as well.
We usually consider replication or fabrication of predefined forms (with challenging technique) a craft.
Are photos art because they are easier to make than microsculptures? I don't quite follow your emphasis on the technique needing to be challenging.
All a photo really is: the visual replication of whatever the camera was pointing at when the photographer activated the shutter release. Yet we consider there is art where the photographer chooses what to photograph, how to frame the photograph, and even things like what kind of film to use (black-and-white vs. color, grainy vs. smooth, etc.). It seems to me that similar dimensions of choice were in play when Jonty Hurwitz made the microsculptures: he chose what to reproduce as sculpture, what poses to use, what scale, what materials the sculptures were to be made from, etc.
Would your position on the microsculptures change if the Jonty Hurwitz had called them "3D photographs"?
P.S. While we are debating what is and is not art, do you take a position on the dadaist sculpture "Fountain"?
Personally, I think that there is artistic merit in taking a pre-made object and changing how one looks upon it (I doubt anyone had ever conflated a urinal and a fountain before this). However, while it was radical (even shocking) in 1917, anyone trying to do the same thing today is bringing little new to art. If I put an upside-down coffee maker on a pedestal and title this work "Brown Liquid Fountain" I doubt anyone would be very impressed.
If you reject "Fountain" as not art, you are in disagreement with very many people. If you accept "Fountain" as art, then why would you not accept the microsculptures as art?
And if pre-made art is only clever the first time it's done, Jonty Hurwitz is still on safe ground; I've never heard of anyone else doing this first.