Art is subjective and beauty is in the eye of the beholder so to each their own. I agree with you that as far as theme parks go, Disney is mostly designed beautifully. But I also agree with
@MansionButler84 that ultimately these are fake representations from a fantasy world built in reality/central Florida - a lot of these things don't truly exist (flying carpets, Galaxy's Edge, etc.) so ultimately we are criticizing fake elements. In some people's opinion, some of it is tacky. Doesn't mean everyone has to agree.
Personally, I think Cinderella Castle was beautiful with the original color scheme. I still think it's a beautiful piece of architecture but the new color palette was a downgrade in my opinion. And to me, the multi-colored banners on the now multi-colored castle look tacky - there's too much contrast even within just the new paint job and the banners take it all over the place. If their goal was "iridescent," I don't know why they didn't just go iridescent. But again, we can all have different opinions.
It's interesting that we all have such strong opinions about the castle - shows how iconic and beloved it truly is. We all want to see it in it's absolute best and we want the Imagineers to serve it love, respect, and the justice we all think it deserves. But as far as art goes, which the castle ultimately is, it's really subjective so we all have a different idea of what the castle should look like.