To me, this says that it's the composition that disturbs you. Many people have pointed out that Klimt was threatened by women which is why their hands always look like claws. He also clumps his humans in with abstract color, but it's "human" "abstract color". He follows the rule of thirds, his compositions are balanced. Mucha used color and ornament to great effect (combined with photorealistic faces) and your response is "commercial." Which, yes, they were. Although I'd be curious as to how you regard the Slav Epic: Regardless, it's clearly not Chagall's use of color that disturbs you. Your reaction to Giacometti cements my thinking. Giacometti is all about framing in that he eliminates all but the human form, warped. You can't help but regard his art as a play on framing as you must regard it in relation to yourself. Chagall frames in a deliberately random-looking way. You find it disquieting because he's aware of the rules and distorting them for effect. You find that effect displeasing because framing is an important part of your artistic style... in the direction opposite Chagall.
I think that's close to the mark. Yes, I'm not much bothered by Chagall's use of color. I don't love his palette, but I do find his non-traditional composition to be icky. It creates a reaction. The Slav Epic looks amazing. It's probably pretty clear from my own paintings that I am not much into unbalancing the viewer, at least in terms of composition. I definitely wouldn't accuse Chagall of having a schtick. It's clearly coming from aptitude and experience. The schtick/style/voice space is one that is interesting to me. It's also interesting to me that there merit in being original, and being genuine, or at least in the ability to create controversy around it. I know that plenty of artists explored that space. I guess proof to your point, is that I'd much rather hang a Kinkade than a Chagall.