Casablanca is the ultimate product of the studio system--established stars, contract supporting players, seasoned director, experienced composer; solid technical craftsmanship without calling attention to itself.
Citizen Kane is the ultimate individual film--lead player in his first major film; supporting players from the stage and radio, inexperienced director, first-time film composer; experimental techniques in photography and editing. As close to an independent film as one can get within the studio system.
Hardly! Cast and crew were entirely from Warner's top shelf. B-movies were low-budget quickies that the studios pumped out for the bottom half of double features.
When CASABLANCA used to run on New York television in the 1960s, the NY Times capsule review was "Never so much golden corn." Obviously the movie has risen in general esteem since then. A Humphrey Bogart cult following at Harvard University in the mid-1960s may have marked the beginning of the trend.