I would love to see that "deep spectrum analysis" and evidence.
Yeah, me too! (joke ^^). You can do it by yourself using
Audacity's "Plot Spectrum" effect, with
this classical music video in example, remembering that it requires you to find a moment where a single instrument is audible at a time.
I don't have Audacity installed at the time, but there's something much worse related to 'youtube' and similar services. Namely it's high lossy compression totally ruins the sound quality and flattens it to 128 kb/s M4A (or AAC), what's even worse than medium-quality 256 kb/s MP3. You can't compare it in any way to WAV's or FLAC's 1411 kb/s, but nobody should be surprised while 'youtube' was never designed for music sharing, nevertheless most people started doing so because it's very convenient, free, and they have no idea about the codecs, bit rates and the quality, or they just don't care about it.
I'm sure that most people would hear and even feel the difference, if they just compared a specific song from the original CD with 'youtube's counterpart. I believe that Music is a wonderful phenomenon which should never be disturbed, and people should hear it as it was recorded, considering the quality of sound.