For Korea, a PoD before Nobunaga and Hideyoshi gained influence in Japan (and replaced by trade-oriented individuals) would have been more beneficial over the long run, as the Imjin War would have been butterflied away, and could have theoretically prevented the Manchus from conquering all of China, due to both the Ming and Joseon making more adequate preparations for decades. In previous threads, I've extensively covered
why Korea's overall situation began to largely stagnate by around 1800 or so, as well as detailing the effects of a Korea with larger demographics (and that's just within the last five months or so), eventually leading to incremental changes for over two centuries.
That being said, a PoD by 1750 or so causing major migrations away from the capital (presumably sponsored by the government) could potentially enable more urban areas to sprout up across the country. This could ultimately lead to to a more consolidated Joseon that is able to sufficiently deal with Japan (as well as China and various Western Powers) diplomatically by the late 19th century, eliminating the eventual economic, military, and social pressures that were gradually imposed upon the peninsula after 1876.
In either case, the divergences may then collectively cause China to assume more equal relationships with Korea and Japan (and possibly with Europe as well) by the 18th-19th centuries (although they might still remain as tributaries on paper), and in turn potentially benefit Vietnam as well, making it viable for the country to resist French colonization.
Instead of closing off and becoming isolationist, asians (not just east asians but south asians as well) look outwards and make discoveries and expansions of their own in the new world, africa, and australasia.
European dominance of the world was nowhere near inevitable. Rather, a more likely outcome would have been the East China Sea and Indian Ocean countries due to their historically greater wealth, innovation, and population sizes prior to the Renaissance.
How, exactly?
Various threads have covered these issues for years, and the general consensus is that European countries had significant incentives to gradually expand along existing trade routes (by utilizing preexisting knowledge of ocean currents) over decades, if not centuries, due to middlemen essentially functioning as a monopoly for trading with South and East Asia, eventually leading to an excess of demand. On the other hand, various entities within South, East, and Southeast Asia had more than enough supply to match their collective demand for well over a millennia, as all of them traded extensively with each other, even among disparate regions, causing general reluctance to European colonizers (as the latter initially had very little to offer). Additionally, attempting to directly expand into other countries would have been extremely difficult due to logistics, economics, or politics, as the governments involved would have been unwilling to significantly increase their expenditures when they had continued to profit for generations.
Additionally, all of the countries in the three regions were frequently preoccupied with wars in inland frontier regions, and there is a big difference between "fending off" invasions from Europeans, and "expanding into" regions that a particular country already has stable trading relations with, or sailing into ocean currents that generally work against them.