Originally Posted by M.Bonanni

If we're speaking in general then I disagree, especially if you don't have a wide array of spring rates/dampers/alignment tools/tire sizes/etc at the track which I am sure none of us do. Sometimes you have to stiffen up the rear sway to compensate for other parts of the setup or even conditions. A super bumpy track with a lot of tight turns might be an example. You wouldn't necessarily want really stiff spring rates yet you would want to stiffen up the rear to rotate through the low speed corners. Keep in mind I am talking in terms of using off-the-shelf parts not fully adjustable fully custom real race car parts. Sometimes we have to make do with what we've got access to which isn't always the ideal situation.

Now if we're talking about the OP's case in particular then I don't think he needs to be full firm on the rear sway at all, I think that is the problem, or a large part of it. Toe issues under load would likely feel more squirmy and unpredictable (like this ) or even result in snap oversteer and not a gradual predictable mid-corner/exit slide. A broken shock would also not be a gradual and predictable loss of traction plus handling would be different in right handers vs. left handers and it would also be felt under braking as the broken side would not be controlling the spring. Shocks settings is the next likely issue but I still still think its a combo of the rear sway being too stiff and application of the throttle being too early which is breaking the rear traction. It's the fact that the oversteer is gradual and predictable that makes me think its handling balance/driving related instead of a mechanical issue.

Anyway, just my two cents. Hard to say anything for sure without data or driving it myself.