A fair point. This list has 468 above 1 million and I think that's the urban boundaries and not metro
I hadn't actually googled concepcion, 200,000 in the urban area is quite small. It would be interesting to somehow workout the percentile of population living in a larger/smaller place.
Look at the UN 2019 population estimates and sort by it. The last 10 areas are
5.49m, 5.49m, 5.38m, 5.38, 5.30m, 5.21m, 5.16m, 5.09m, 5.05m, 5.02m
Given how curves like this usually go there's an extremely long tail to get to 1m
Concepcion has only ~200k people with <1m metro. Looking at a map of the city and with only 200k people it doesn't seem big