Not entirely. Frankie said that Kazuma is doing most of Halo 5's music, not only do they have several hundreds of minutes-worth of music that Neil did that wasn't in Halo 4, but there's been nothing directly stating that he's out. It seems more like they've done a bit of a reversal - H4, Neil leads, Kazuma does less. H5, Kazuma leads, Neil does less.