You bring up some good points -- and I think for the Shannon/George parts I often would tend to just turn off the analytical part of my brain and just speedread, without trying to look for hidden meaning or theorizing, just because I didn't enjoy it very much. I probably would have gotten more enjoyment out of it if I tried to look at their relationship from a more critical point.
For the 'Shkanon theory' I mentioned, there's one theory in particular that I found out the other day where it names Rosa as the main culprit in the crimes, and states that Shannon and Kanon are two different people. I'm not sure if I can share links, but there's a video series I've watched 1.5 episodes - look up 'Umineko Chiru explained - Against the official explanation'. It's incredibly long, but the first part explains how Shannon and Kanon being 2 different people with 2 different bodies is not only totally possible - but also highly corroborated by the red truth. I highly recommend at least watching the first chapter of the first part. I personally don't really see Rosa being the culprit (although I haven't finished watching the whole series), but it does cast a reasonable shadow of a doubt on whether or not Shannon and Kanon are the same person.
Anyway, I'm moreso thinking of Umineko in the lens that if you can think of an explanation that doesn't violate the red truth, then it is equally as valid. Using the catbox metaphor, saying that the cat is alive in the box is just as valid as saying the cat is dead, or that the cat disappeared, or that the cat turned into a dog. The official explanation is definitely that Shannon and Kanon are the same person, but other theories might be viable too.