Yes Bryce. I think also there's possibly less of a cat-and-mouse battle between Columbo and Ruth. Many of his adversaries seem pretty obnoxious, and rather willing to play along with him, as a way of detracting attention away from themselves. They can be rather smug and a little vain, and all to eager to portray a rather false facade. However, one gets the feeling with Ruth that she, more than anything, sees the murders as a kind a statement. I'm not implying, for example, that she wanted to get caught, necessarily, but there appears, perhaps, to be longing of recognition on her part, that she's entitled to a life as well, and just as her sister has managed to cause her a great deal of hurt, she's not incapable of administering the same.
I believe the portrayal of Phyllis being almost cartoon-like in her eccentricity, was simply a way of showing the utter contrast between the sisters, within the time available. Celeste Holm's character may have seemed unbelieveably extreme in her fainting etc. but there's also a sense for me, that the comedy elements within her performance (and that of Daryl too) marks a nice contrast to the overwhelmingly deep psychological overtones of the rest of the story.
I never really saw an issue with the casting of Jeanie Berlin, either. She could just have resembled her father's side of the family more. I know plenty of 'real' families where resemblances between certain members of the family, are not always strong.

I had never thought about the Phyllis character that way before, but now that you mention it, Edward, it is a nice contrast from Ruth, and sort of shows that while Phyllis over-reacts to the slightest things, Ruth is very reserved, even though she has deep-seated anguish far more oppressive than anything Phyllis has had to endure. So in a sense, one sister has petty pain, yet responds to it mellow-dramatically, while the other has torturous pain, yet expresses it meekly. Well, until she reaches a breaking point and commits murder.
One thing I wanted to mention again is the music in the episode. It is very distinct, much like the themes to "Murder By the Book", "Ransom for a Dead Man", and "Any Old Port in a Storm"; these all have themes that are only heard in a single episode (although I believe "Ransom's" theme can be heard quietly as background music in a few other episodes). Also, much like the Patrick Williams scores for later shows, I feel "Old Fashioned Murder's" music really helps set the mood.