I think we need your definition of “high quality” to help answer this question for you.
If your definition is “perfect reproduction of the source audio” or “zero noise floor”, then I think you’re 100% correct. The Mogwai is not a high quality amp with those definitions and if those are your goals, I would agree that you should avoid the Mogwai like the plague. Also avoid any vintage amp by McIntosh and DIY kits from companies like Bottlehead. All these amps change the sound of the input, may introduce noise, and some even add very noticeable distortions. Also avoid turntables because they need to be grounded correctly and sometimes, even when grounded, have a noticable hum when the volume is turned up loudly. Also avoid high sensitively speakers like those from Klipsch because their horns often have an audible hiss, especially if you pause the music and put your ear right up to the speaker.
If your definition of “high quality” is “built with high quality components” or “built by hand in a way that could be repaired for a lifetime by anyone” or “produces sound in a pleasing way to my ears”, then it could definitely be argued that the Mogwai is very high quality.
Noise is very much a subjective thing and some people really don’t care about minor noise because they enjoy everything else about the experience. Some other people (like youself) DO care about noise and that is also totally fine, but it doesn’t mean the product is “low quality”.