Paul Strathern's The Medici paints a very Faulknerian image of a bleak and decayed Tuscany under the later Medici Grand Dukes, but I also understand that Tuscany, and Pisa in particular, was an important center of the Romantic movement. This is not necessarily a contradiction (if nothing else, there is a gap in time) but based on other aspects of the book I would not be surprised if Strathern's image of post-Renaissance Tuscany was simply a distortion.
I haven’t read Paul Strathern's The Medici so I can’t assess specific claims, but there are a few things we can look at to judge how vibrant of a society Tuscany might or might not have been once the Italian peninsula’s heyday was behind it.
If we want to look at simple economic prosperity, according to the best estimates we’ve got (the Madison Project) Italy doesn’t look half bad right up to industrialization, topping the European tables for economic output per capita until England and the Netherlands take the lead in the 18th century (and nonetheless staying in a comfortable third until the 1820s). In this “not half bad” ranking, Tuscany is an important component.
The Maddison Project’s main contributors for Italy in the Early Modern period are works by Emanuele Felice, Paolo Melanoma, and Jan Luiten van Zanden, who all actually exploit an emphasis on Tuscany in their work. Specifically, Felice and Van Zanden’s “Benchmarking the Middle Ages. XV century Tuscany in European Perspective,” admits a bit of an over-reliance on Tuscan records for pan-Italian estimates, but argues we can use Tuscany as a stand-in at least the North of the peninsula - which I guess we can allow although other literature might argue that income per capita in Tuscany was slightly higher than in the rest of the peninsula in this phase. This is because the best GDP-per-capita outcomes consistently occur in societies with lower agricultural output where workers are scarse and can drive up wages, but also conveniently close enough to high-agricultural-productivity areas that can support urban communities where workers can earn those wages in the first place; that’s what the whole of 18th century England pretty much was, and also what describes Tuscany, which while hummocky and mostly pastoral nonetheless was able to import resources to support vibrant and competitive cities.
After 1500, we can more easily accept the idea is that Tuscany-reliant estimates stop “boosting” the rest of the peninsula and instead start “representing” it as analogous high-productivity area have now enlarged elsewhere on the peninsula: trade networks and prosperity in the Northeast spread out from the Venetian Lagoon, Liguria become a massive maritime suburb for Genoa, and while Lombardy doesn’t fare well for the next fifty years due to near-constant warfare, there isn’t actually anything to lead us to believe its productive urban communities were displaced (Milan was still being described as Italy’s “Principal City” in the early 17th century, in spite of the damage of war). And this analysis is simplified by the fact that Italy industrialized late. If we were writing about England, we’d have to introduce a narrative about the beginnings of economic expansion experienced in some parts of the country, whereas for our purposes we don’t really need to introduce notions of industrialization until after the Napoleonic Wars. If we want to, we can acknowledge that Tuscany, while not arriving at Italian Unity as the worst industrializing region in Italy (and was actually located towards the top of the bracket) was nonetheless miles behind the Northwest. So to keep in mind that maybe, in the period we’re examining things are happening (or not happening) which will cause Tuscany to soon start to lose economic grounds.
So that's my real wheelhouse - economic history. But what about intellectual or cultural history? I've added a second part to this answer below to examine just that.