Peter my questions answers most of that. There's so many different platter materials these days.
The problem with just trying to know if the stylus affects it or not is that, well, you can't see it. But if we know that say there is a consistency with a difference in sound with ones that slip easier, we have something of interest. Hence just testing with fingers. (it's just the reverse of what happens when you turn a turntable on, odds of damage aren't a concern, and belts should slip not stretch unless set too tight)
Weights will affect the outcome, for sure. The consensus on here is that the manufacturer of a turntable has worked with concerns of conditions that would make a mat useful. In other words mats are not appreciated since the assumption is the manufacturer dealt with the issue, especially when it's an expensive TT. In some cases that may be true, but for a lot of TT's it simply goes against physics. The sound from the stylus going into the record, down, then back up, is something best eliminated. The metal platters for that reason make little to no sense, except in subjective points.