The answer is subjective, and really going to depend on how you personally feel about stereo separation, and how important you feel that the soundstage should be completely in front of you.  And to be clear, the reason that soundbars exist, instead of separate left-center-right speakers in not for sound quality, but for cost, ease of use, aesthetics, etc. 

I don’t think your view is unreasonable at all.  Would I rather have a pair of ones+ sub instead of a Arc+sub for music playback?  I don’t know.  I do think I’d take the ones +sub over a beam+ sub for sure,  I have Beam+play:1s+sub in my bedroom and have thought about removing the play:1s to use for music,  since I rarely use them for surrounds.  The main reason I don’t is because I want to use the sub for both TV and music.

If you want good audio quality for both movie and music, then I suggest that you part with the Arc, buy a Sonos Amp and pair it with two good speakers. There is no way a soundbar can compete with a pair of decent bookshelf in delivering superior sound. For the lower frequency you already have the sub.