Lighter/heavier weight is only a detriment if two vehicles are identical in every aspect. If someone took my current mini which weighs 1250g, and swapped my peak 4200 for a much lighter pack, the settings would be totally out of whack.

A completely stock planetary gear actually oversteers, as the differential is "differentialing" too much. The planetary gears absorb the kinetic energy of the car and slow down the rotation of the car during this left to right energy transfer, which is why a car with a front diff is usually easier to drive. Due to the law of diminishing returns, a diff will eventually "diff out". This is when the outside tire balloons, as all the kinetic energy has been transferred to that one side. The inside wheel will not lift because your car "diffs out". It lifts because the suspension has not been properly setup (too soft, too stiff, too much droop, not enough droop, etc). In fact, if the inside wheel lifts up, it should have less resistance and therefore balloon up.

The key is for the diff to be stiff enough to keep power on the wheels moving forward through turns, but have just enough give to absorb a little energy. Laps times increase, and tire wear will decrease as a result. For this reason, i chucked the spool last year and went with a "Chuck diff" - which is kinda like a "Scott diff", but with pink Sakura screws.