In any performance medium, the accompaniment exists to support the solo. The volume of the accompaniment should be soft enough that it allows the solo to predominate, yet loud enough that the solo is well supported.
If we must lean to any one side in the volume continuum, it should be towards the “very little contrast” side. “Great contrast” in an accompaniment really means either “little support for” or “overbalancing” the solo, both of which are unacceptable.