I literally do not care how codependent Sam and Dean are .Its not problematic because its a TV show . People watch TV to escape from the real world . You are supposed to be brought into a different world that usually doesn’t exist.
The codependency is not new in the Winchester world. Mary made a deal with YED to bring John back . John devoted his life to finding what killed Mary. John sold his soul to save Dean. Dean sold his soul to save Sam. Dean killed death to save Sam. Sam begged cross road demons to take him instead of Dean. Sam became hellbent on killing Lilith ( just like John was hellbent on killing YED) Sam refused to give up on curing Dean from the mark and told Dean he would do it again.
The codependency is not healthy . But a lot of stuff on television isn’t .If I want to watch healthy , non-problematic shows ,,,I would watch the Disney channel.