I'm quite aware of what the Linux "community" and it's sub-communities are like. However, KDE is messy, over-designed, and comes across as over-engineered. The fact that it's had so much issues with stability, the fact that some of the components (PIM stuff) use gobs of RAM even when you've never used anything associated with them, the fact that KWallet interrupts you continuously and the common "fix" for it is to go through the wizard and input a blank password? The fact that toolbars in applications have icons of different sizes, text placed in different ways IRT the icons (and overloading some controls that contain icons, which display the text in there by default as well). The fact that they show underlined Accelerators all the time, instead of when the Alt-Key is Pressed or Depressed to lessen visual clutter (and it looks messy).
There is nothing wrong with giving feedback on things that are "off." If they only hear "it's great" then nothing would actually improve. They'd just keep adding more crap on top of the bloat.
KDE dropped a lot of features going from KDE 3 to 4, but they've been adding features since then because KDE 3.x users keep complaining that it's worse because they lost features.
Features don't make a user experience great, if they aren't polished. Simply throwing more visual stuff on the screen doesn't make a UX great, if it isn't polished.
I personally don't think KDE 2-3.x were all that good, personally. I do think 4.x (and 5.x looks much better than it used to look) and the code is a bit tighter. But it still comes across as messy.
If I looked at a KDE desktop with a couple of applications open, I would automatically assume that it's F/OSS because it has the typical lack of attention to detail that I tend to notice almost immediately in software from that camp.
This is stuff that Apple would either never let out of the gate, or would fix immediately when made aware of it.
Even Google is updating their Android Launcher to normalize Icon sizes, for example, cause Android had the same issue. It's jarring to look at, and very noticeable.
That being said, third party applications like Firefox, LibreOffice, etc. on Linux are much better.