The guitar can serve the song in any tuning[including standard].it is the skill of the practitioner that is important.
The Concertina is an instrument,that also serves the song,if used skilfully,but the accompanist, does not have the benefits of open tunings,yet still it is achieved.
open tunings do have certain advantages ,they also can have disadvantages.
IMO   the Guitar fulfills its full potential when all tunings are explored properly[including standard ]and used.
open tunings are not the be all and end all,but, they are useful. Dick Miles