It's possible that the shader setups might be slightly different for each renderer which might explain the discrepancies between each Renderer's shader quality results.
That said, Vray and Redshift, while faster than the others (CPU(+GPU?) and GPU respectively) also look underwhelming esp where transparent Shaders are concerned. This is persistent with my own experiments with these two renderers.
Octane is finicky at times but just like Arnold, I prefer it's out of the box results. Octane's transparent shader results look the sharpest and to me, the most believable. Even Arnold is muddled in some of these results ( not to mention the less than stellar rendering times )
PS: How did you setup Renderman 22 for Houdini? I have installed it but I don't see options that are different than the existing integration of the 20/21 defaults in Houdini.