Gloria vs Gloria

I don't understand why the vast difference between Gloria in season 1 and Gloria in season 7. I can handle different actors, I can even handle minor changes in character traits, but this was far beyond minor differences. Played by Doris Belack ("The Custody Battle", season 1), Gloria was sweeter, more likable, and she and Dorothy were like best friends. Dena Dietrich's Dorothy was bitter and sarcastic, and Dorothy couldn't stand being near her. The bitterness was somewhat believable since she had just lost all her money, but the earlier Gloria probably could have handled it better for being so strong and level headed. I couldn't even fathom her in bed with Stan.