Controlling room reflections is first port of call, as these are nigh impossible to correct with an RCS. But also RT60 and reducing impact of standing waves is better done with acoustic treatment. RCS should be 'the icing on the cake'
3D, dipolar speakers have very little sideward energy, so are great if you want to place them close to a side wall. Also, the dipolar nature of the bass greatly reduces bass problems in most rooms, if correctly placed in regard to the wall behind the speaker.
Tensen, indeed will you correct speaker response with an RCS, but if there is less to correct, the end result will probably be better... When some dips in the speaker are phase related for example, correcting them with RCS could have nasty effect (just an example). Amplitude aberrations of the speaker are less of a problem them time/phase problems.