Centre-channel cancellation and what it costs
The technique removes everything centred, not just the singer. Bass and kick drum are almost always centred too, and often the snare, so an aggressive setting can hollow out the rhythm section along with the voice. That is why strength is adjustable rather than fixed: a moderate setting reduces the vocal enough to sing over while leaving the backing recognisable, and the strongest setting removes more voice at real cost to the rest. Listen to the whole track rather than one chorus, since density varies across a song.