Remember that these are the city figures only, not including the surrounding metro and urban areas. This is why cities like Manila and Paris are much less than expected as they are using the strict city limits. (Just search Manila population on google, it's that number being used!)
The problem I was having was that not every capital had figures for urban areas, which meant that it was difficult to decide which figure to use. That's why I ended up using the figures supplied by wikipedia's List of National Capitals by Population. Because that way it's whatever wikipedia has decided to sort them by. Thank you for the concern though, I'm sure others were probably thinking a similar thing!
Yes I know it's not easy for things like population so often it's best to just use a list that has already been made - but sometimes they do have mistakes/incoherences. What about London, I don't actually know but perhaps "technically" wikipedia has considered the urban area population for it? https://en.wikipedia.org/wiki/London
Yes, I see what you mean about London. However London City's borders are defined to be large, which means some of the Urban area may already be included in comparison to other cities. I think, for now, I will continue providing the list provided by the wiki, albeit the inconsistencies, it seems to be a relatively fair list to use.
If manila makes it, since that city has like 30 million people, then how is Jakarta not on here? It has around the same population as manila but indonesia has double the people. From other countries on here it would assume that your using urban.