When you compare music of the same genre (Or sub-genre for that matter) using the target audience, the quality of the music becomes objective. Take, for instance, Body Movin' by The Beastie Boys. When it was released on radio, it did not do well. The song was said to be lacking in element and flow. Then Fatboy Slim came along and gave it a remix. The song suddenly was on the top of the charts in hip-hop, dance, and rock stations and stayed there for quite a while. The remixed version was outright better, and not even the Beastie Boys defended the original (they in fact added the Fatboy Slim remix to one of their favorites albums). Country music fans couldn't give two ****s about the genre, so their views on it are subjective.
Oh, and I'm no fan of country music or rap, but I can still objectively judge the quality of the song by following the basis of music theory and composure. I being a big fan of hip hop, but no so big a fan of metallic punk rock, I still know How I Could Kill A Man was performed much better by Rage Against the Machine than by Cypress Hill. Rage gave the song lots more consistency and uniformity. Subjective? I think not.