I remember being very glad Lucy Punch didn't stay for s2. I think the writers would have had to modify her character a bit if she had stayed don't you?
I think the most successful characters are complex. Elaine was essentially one-note, and not a very nice one at that.
Bert Large could be a buffoon, but we see his devotion to his son in the episode where Al questions his paternity. We see it when Bert brings the baby carriage to Louisa. Buffoon, hypochondriac, scheming, Bert is all those things, but never cruel.
In contrast, Elaine was so self-absorbed that I didn't care about her pain from her Father's remarriage.
Hope that makes sense.