To some extent this is an optical illusion because we have the individual names of almost all Western artists and scientists since maybe 1500. Since we don't have the names of many of the artists involved in Gothic Cathedrals in the Middle Ages, it's easy for pundits to overlook them. Similarly, we only have a vague notion of who was chief architect of the Shah Jahan's Taj Mahal in the 17th Century.
But, most of the rest of the world was indeed stultifying after 1500, with Japan as an exception that was making steady progress.
The problem with creativity, is that we feel that we know it when we see it, but it's hard to quantify in the present, much less predict in the future. IQ has been studied intensively for a century, and we now know that it not only works pretty well in the present but as a predictor of future developments (e.g., Ian Deary's recent work tracking down surviving Scots who took a national IQ tests as 11-year-olds in 1932). And it seems to be fairly heritable, which probably is the chief reason we relatively few radical changes over time in national average IQs.
Creativity remains somewhat difficult to measure in the present and notably hard to predict in the future, with various national golden ages of this or that happening regularly.
Charles Murray's Human Accomplishment art and science creativity metrics work reasonably well in hindsight, leaving a half-century lag. Yes, Beethoven, Mozart, Bach, and Wagner were creative. No question about it.
So, because the most creative is the most unexpected, I've usually been less eager to opinionize about the future of creativity than of intelligence. Of course, it's because scientists know more about intelligence than creativity that we aren't supposed to talk about differences in IQ.