What is wrong with you? Chicago shall always be the Second City.
Not at least since some time in the 1980s...
Population has nothing to do with it.
Is Chicago America's second most important or influential city?
Los Angeles is an amalgamation of suburbs that doesn't have much of a center. Chicago is the only city outside of NY with a skyline that at all approximates Manhattan.
Since Los Angeles is a decentralized suburban agglomeration it is more like Tokyo in character. And people love to point out that there is no "Tokyo" the way there is a NYC or Chicago.
Neither LA nor Houston have anything approximating the Chicago skyline...but then LA may one day surpass NYC in metro pop. Will NYC then be Americas 2nd city?