Okay so there’s sort of two parts to this question – do we expect developments in the history of art and technology in the Pokémon world to mirror those of the real world, and exactly how much do you know about ancient portraiture?
I don’t think it’s totally unreasonable to assume that the Pokémon world has a similar history to our world except where we’re told otherwise – but we do keep being told otherwise, about more and more places and periods. Personally I think it’s an odd choice – AZ’s kingdom and the Kalosian civil war seem to reference both the aesthetics and the ideological conflict of Enlightenment-era France and the French revolution, so it seems incongruous to suddenly be told that they actually belong c. 1000 BC. They’re definitely allowed to do this; there’s no reason that the Renaissance and the Enlightenment need to have happened in the Pokémon world (if nothing else, the fact that the Roman Empire doesn’t appear to have existed would throw that entire millennium off the rails). It’s definitely strange to think of this civilisation predating the Ruins of Alph by over a thousand years, though, or being contemporary with Hoenn’s Primal Age and the destructive reign of Kyogre and Groudon. But these are totally different regions, after all, and we have no idea how far away they are from one another, or whether they were in regular contact during that period.
Anyway as for the Greek pottery and bedrock murals – those are not, by a long shot, the only or even the most common media for portraiture in the kind of era we’re talking about. I don’t know East Asian archaeology, like, at all, so let’s not go there, but the Mediterranean and Near Eastern Late Bronze Age (c. 1500-1000 BC) is hardly just cave paintings. Look, for instance, at fresco from Knossos or Pylos, or stone relief carving. I assume by “Greek pottery” we’re mainly thinking here about Attic black figure and Attic red figure, which are actually not very common but are certainly the most famous types of Greek pottery, as well as the most distinctive and the easiest to date precisely. These are much later than 1000 BC (625-350 BC is their heyday, more or less, and they’re actually very odd – it’s extremely rare, both before and after that period and across most cultures, for pottery to be used as a medium for narrative art or depictions of the human form). They’re also never the primary medium for portraiture; we love them today, but ancient writers talking about fine art never mention pottery, and wall-painting and panel painting were actually way more prestigious. Portraiture more similar to the kind that we’re familiar with from the Renaissance almost certainly existed, it’s just that it was primarily done on wood, which doesn’t survive archaeologically for 2000+ years except under very favourable conditions. Now, in Egypt you sometimes do get very favourable conditions, and if you look up the Fayum portraits you can see exactly this kind of thing in the Roman period; those are part of a tradition that goes back at least to Classical Greece. So what I’m trying to get at is that although it’s legitimate in some ways to say that it’s odd to see an Enlightenment era style in 1000 BC, it’s a bit presumptuous to dismiss art of the 2nd millennium BC as just pots and cave paintings.