I disagree about the wife, in the sense I think she's good looking, however not a very good person obviously with the reaction to bertie's death or "not wanting to understand" oliver's embezzling problems, and for this reason I liked his answer in the end (keep in mind I watched all columbo episodes in italian, so words might differ a little in the english version): she asks him to come home to bed with her and that she needs him, and he answers "unfortunately I doubt I'll need you any more... for a while" and hangs up.
I also don't find those compliments columbo made creepy, on either episodes.
Indeed, the monologue about the umbrella was strange and I'm guessing it made him even more suspect in columbo's eyes, also agree that for a genius he didn't make it difficult for columbo to catch him.
Lastly, I don't think the sigma members are stupid, just eccentric, which oliver says as well; the president danziger in particular, and I liked the ending, when oliver calls them stupid or something along the lines: columbo answers: "the president danziger, you can't call him stupid", "why?", "cause the idea of the book was his, vibrations" "vibrations? What are you talking about?" "of the first squib that exploded, he explained it to me in the easiest way: when the squib exploded it provoked some vibrations and that's right what made the dictionary fall! That danziger's a genius!", and then ofc brandt incriminates himself; columbo knew this theory was crazy and gave danziger credit for it, and brandt couldn't stand that and that's what led to his fatal mistake!
Overall, it's one of my favourite episodes, I also liked that problem with the sacks of gold.
You did such a great job of describing the ending of the episode that I could almost hear Tcaichovski playing as the veins in Oliver's forehead bulged out, lol.
And yes, the wife is physically attractive, but what a nightmare for a life partner. As evil as Oliver is, he embezzled and killed Bertie to keep HER happy, and she won't even let him finish his sentence.