Yeah, that's Tolkien's ethos alright. One part rejection of the modern industrial world and the horrors of World War I, one part a particular line of Catholic thought holding that the world was perfect at the beginning in the Garden of Eden and it's been all downhill since. For better or for worse, Middle Earth was his personal creation and it really reflect him. It's just, being one of the foundations of a new genre, his every little quirk got encoded as a new tradition.
Well, it isn't just
a Catholic notion there. Europe still carries the legacy of Rome. I relatively recently learned how much Europe collapsed
after the end of the Roman Empire--with some cities literally collapsing into occupying just the amphitheater
, and that being sufficiently spacious to hold the whole town's population! And the Greeks themselves often saw themselves as the weak, feeble, flawed descendants of an ancient, lost golden age, with the preceding era of Greek culture being seen as the last echoes of that bygone age of greatness (that is, the era of the Homeric myths.)
Idolizing a forgotten past is a pretty common European thing, and I'm fairly sure it's found in Chinese myth as well (but it's been a while, I could be mistaken.) With Europe in particular, it really was
the case that for something like 800 years, they couldn't really match the feats of engineering and architecture of the ancients, and it's taken modern science for us to figure out some of the things that made their work so durable (e.g. the recent discovery of the self-healing properties of Roman concrete, or the slightly less recent discovery that using seawater in concrete can make it dramatically harder.)
Consider the enormous amount of ancient literature lost in Europe but preserved in the Arab world before returning through Al-Andalus, and the nearly-unquestionable status of thinkers like Euclid, Galen, Plato, Aristotle, Archimedes, etc., and you get a justifiable sense in which the "great works" of the ancients were difficult to surpass for an age. It wasn't that they couldn't
be in principle; it's that their society was built on a higher degree of infrastructure and organization than medieval Europe could support. Coupled with the difficulty of preserving the knowledge and technologies of Antiquity, even if people did
make advancements, it was hard for those advancements to have major impact. Not impossible, just hard.
All that said
, it is something of a Euro-centric perspective to put SO MUCH emphasis on "the ancients were just, like, WAY cooler than us." There's a place for that, to be sure, but there's a place for the world getting better. My setting has something of an advantage here; the "ancients" were the ancient Genie-Rajahs, who were powerful because they have innate
magic, and who abandoned the world a couple of millennia ago. They took basically everything except the cities themselves with them, so the mortals they left behind had to rebuild their society themselves. Not quite "from scratch," but definitely a lot of effort. There have been setbacks and blind alleys, but by and large, mortal society has been successfully putting itself together and getting stronger rather than weaker. Much, much more is known by mortals
about magic than the ancients could have known.