They may have access to a magnification technology but what would be the objection to the idea that human eye had a closer focus point 3000 years ago?

I'm open minded but in terms of evolution, 3000 years is a very short time, so changes in human physical capabilities requires specific and compelling evidence. In contrast, bronze age mirrors certainly existed and noticing and leveraging the effects of non-flat surfaces seems fairly inevitable to me given you only need to look at a spoon or something.

But it could be a one off. That is, someone was born with a mutation that gave them amazing levels of visual acuity, but didn't pass on that trait to children.

3000 years is to soon for significant changes in human DNA. Every population world wide would have to have very strong selective pressure for such a change to occur. Alternatively, everyone worldwide could simply have some environmental difference resulting in changes to the eye, but that also seems unlikely.

>3000 years is to soon for significant changes in human DNA.

Doesn't necessarily has to be DNA. Prevalence of fixed focus work, screens and monitors and reading, has made more people need glasses, in earlier ages, than 100 or 200 years ago for example...

Could it be the prevalence of ophthalmologists instead? I assume it was really hard to get good medical care100 to 200 years ago, not to mention the cost of glasses.

>Could it be the prevalence of ophthalmologists instead?

It's orthogonal. More doctors would mean more diagnosis. But more short distance indoors fixed focus screen work stress on the eyes would also mean more patients.

Too little time outdoors

Research has found that spending time playing outside as a child may reduce your chances of becoming short-sighted, and existing short-sightedness may progress less quickly.

This may be related to light levels outdoors being much brighter than indoors. Both sport and relaxation outdoors appear to be beneficial in reducing the risk of short-sightedness.

Excessive close work

Spending a lot of time focusing your eyes on nearby objects, such as reading, writing and possibly using hand-held devices (phones and tablets) and computers can also increase your risk of developing short-sightedness.

An "everything in moderation" approach is therefore generally recommended. Although children should be encouraged to read, they should also spend some time away from reading and computer games each day doing outdoor activities.

https://www.nhs.uk/conditions/short-sightedness/causes/

Not everyone worldwide has a computer. The environmental change I mentioned would need to be something like the change in CO2 levels to impact everyone.

You can't use "small details" to logically arrive a higher focus point. What use would humans have for intense detail, at a time when the world was far more dangerous at range? And even then, 3,000 years ago is less than a blink of an eye in terms of evolution. Without more examples of humans actually "needing" intense, closer focus, there's no way (even with a 3,000 year evolution window) they'd evolve closer focus just for... art.

Occam's razor is rather applicable here. Magnification would be way easier and more available. Even a polished bent sword magnifies.

But even if you can see the work, how do you stabilize the microtremors in the artists' hands?

You can use the equivalent of a mahlstick to guide your tool. Its one of those sticks with padded heads that painters rest their hand on to steady it.

https://en.wikipedia.org/wiki/Maulstick