Of course mechanical components are the weak link and always have been. But that's not what you originally said - you proposed that it takes a special amp to enjoy an LP when the amp is far from the weak link.
The frequency response of an LP is grossly overrated. Sure there is 40kHz content possible, the first play, and 40 dB down. Since I rather suspect you can't hear 1/2 that frequency, much less that far down, it is moot.
LP's main disadvantages are:
noise
wow/flutter (jitter)
durability
non-linear frequency response
If noise was the only one most of us would never have upgraded to CDs.
Your description of how aliasing comes into play is simply wrong, as it assumes improper filtering before sampling. A square wave is nothing more than a collection of sin waves. A 15kHz square wave can not exist after filtering content below CD's Nyquest, and more importantly can not exist period on an LP. I'd like to see someone draw just how a square (or even triangle) wave would exist on a record groove. Bonus points for demonstrating how a non-theoretical-point stylus can track said groove.
If audible tones are affected by supersonic harmonics they were affected in the studio and said effects were recorded. End of story unless we are talking artificially created tones intended to cause interference only upon playback (See The Hafler Trio).
If we are talking supersonic harmonics designed to interfere on playback, ones which did not exist during recording, then we also must assume you have some brilliant speakers to be able to produce these tones in a linear fashion and not just create a bunch of HF noise.
I can show you plenty of LPs with content > 22kHz, but I challenge anyone to show needledrops with signal, not noise, that high.