Sayas, I think you are on the right track with the "rock solid" comment. However, we are really talking about rigidity there, and a nicely welded-up frame stand can be very rigid.
The reasoning comes from the way the stand interacts with the suspension of the turntable. The sprung turntables just sound better on a lightweight stand, but it has to be very rigid. Flexible-flyers need not apply. Since the mass-loaded unsprung TTs have no suspension, they sound better on a very heavy stand(or even solid rock) because they require the mass to compensate for no suspension.
You're not going to totally ruin the sound one way or the other. It is just a certain amount of improvement. When I used to sell Linn TTs, and a customer would call back complaining that it didn't sound as good as when he heard it at the store, the first thing I'd ask is "What kind of stand is it on?". Invariably the answer was on top of some kind of credenza or other heavy furniture. When we would take a SO stand out to the house and moved the TT onto that, the whole performance just improved noticeably. The same was true for the other suspended TTs that we sold. Eventually we just convinced people during the demo, what stand needed to be used for certain TTs, by showing them the differences in sound of stands during the demos.
This is the kind of thing that you just absorb over the years of experience. I learned this in about 1982.
