Overpopulation is always relative. It means that the population at hand exceeds the amount that existing systems can cope with. You can argue that Indian society is badly organized and that their current population levels and densities could be sustained with better societal systems, but that doesn't quite capture how difficult it is to fix societal systems.

And a lot poorer overall, which certainly doesn't help. GDP(PPP) per capita for India was 7874 in 2018. Versus 41351, 44227 and 53023 for South Korea, Japan and Taiwan respectively. These countries that manage their high population density pretty well are also much smaller (Japan is around 10 times smaller than India) and it is much easier to optimize/organize on a smaller scale.

Japan, Korea or other countries may also be overpopulated yes. But realize the volume spread. A few millions overpopulation is largely different from an over population of a few billions. The magnitude is incomparable.