What would the criteria be to call a city a state? Having an Intl airport? Percent of land mass as compared to the rest of the state? Percent of population as compared to the rest of the state. The population size in number? Presence of buildings over 10 stories?
That argument would never bee decided. Most Missourians would love to get rid of St Louis but is it big enough to become a state? Another issue is that cities tend to grow. Springfield MO is getting bigger all the time.
Then there's metro areas where people who work in the city live. Many if not most of them are dems. The city of St Louis is in St Louis County which is likely all blue.

St Louis itself is pretty small but the metro area on either side of the I-270 loop in St Louis county is likely blue. Muslims have settled in the blue and yellow area up near where it says St Charles County. The East side of the river is IL but is effectively part of the St Louis community and is full blown city like.
The criteria is to have political power, corrupt political power in some instances, to control the politics of the state. In coalition, the City States thus have collectively immense political power.
I agree with everything you said, but the city of St. Louis is a completely separate entity from St. Louis County. It’s a bizarre arrangement compared to the usual city-within-a-county, but nevertheless, it’s true.
There is a unification push from time to time, but it’s a money grab from the city - they’ve lost so many residents and businesses, and people are avoiding going downtown because of the lawlessness of people like Kim Gardner, who will let criminals off the hook.