Vladivostok, irkutsk, tomsk, barnaul, novokuznetzk are all as large as Stockton and not included. In fact there's probably another 15 in Russia that should be on the list.
I expected to see more Russian cities near the top as well. Stockton's city proper population is indeed smaller than those cities, but citypopulation.de seems to lump it together with Modesto and other nearby cities for an urban area of slightly over 1 million. It does feel wrong to list cities like Stockton and McAllen as "major" while excluding Vladivostok, Winnipeg etc, but I don't want to use city proper population and this is the most objective source I have found for urban area populations. Suggestions for better inclusion criteria are definitely welcome.