Why is there no oversampling option in Soothe3?

Because it doesn’t need it.

Many are familiar with oversampling options in plug-ins. Oversampling is used to lessen the effect of aliasing when harmonic overtones are introduced either intentionally with saturation or distortion plug-ins, or as an afterproduct of e.g. compression or limiting. Oversampling can be a very important tool to have when excessively distorting audio, but it can also be deceiving and potentially harmful if implemented incorrectly or just for the sake of having it, when it is not truly even needed.

Soothe and Soothe2 offered oversampling options as well, so why is that setting missing in Soothe3? The answer is that in Soothe and Soothe2, the oversampling options weren’t used for their traditional function of helping with aliasing, but rather for “opening up” the lower frequencies for the processing to be more accurate in the low end of the frequency spectrum. Soothe, Soothe2, and Soothe3 do not introduce non-linearities, so oversampling is not required to combat aliasing. In Soothe3, due to the complete redesign of the algorithm, oversampling is not needed at all.

The “quality” control in Soothe3 is pretty much what the “resolution” control in Soothe and Soothe2 was. Resolution, or quality in Soothe3, dictates the refresh rate of the filters, which is a truly important control to have available.