Modernism and post- modernism has pretty much defined art as being 100% subjective so, yes, MMA is artistic.
If a picture of Jesus in urine ( remember that?) can be art, so can the graceful, yet brutal, display of kicking someone in the face.

Streep's comment was, quite simply, ignorant AND arrogant.
She doesn't get to define what Art is any she has no idea about the ethnicity of MMA ( or anything it seems)