I'm told that historians always view the last while as particularly meaningful and important, and the present is no different. Perhaps this is not the case?

The massive objective changes on the metrics of economics, technology, peace, etc. You just can't generate groups of metrics at the same level of generality with plausibility to naive audiences and make the 13th century A.D. or the 8th century B.C. the most important and dramatically changing in history. And the ancient historians didn't claim that their century was the most important in that way (Golden Ages, etc).

Would super-anti-depressant drugs or gene therapies that made people have very positive affect for extended periods cheaply, and without serious side effects or effective legal restrictions, count as fundamental where all the post-Rome changes don't? Certainly.

OK. This doesn't seem to cut nature at the joints. Why on Earth would the question of whether we've invented a really good happy-drug take such primacy over energy, population, travel, communication, computation, cumulative literature, mathematics, material strengths, height, literacy, life expectancy, etc? Collectively those just seem to pack a lot more relevant info, particularly for the purpose of predicting:

• No nuclear war (although if this is by the end of do-or-die wars between great powers that is itself a substantial change)
• The path of R&D in AI
• That there will not be sustained use of existing genomics and behavioral genetics knowledge for enhancement, and that enabling technologies will shortly begin to stagnate after strong progress
• None of the low probability mega-scale natural catastrophes will happen this century (which we already knew with high probability, but not for this reason)