I'd say "oversimplification", especially if you take a band like Black Sabbath and consider that on their first 6 albums, they covered, in their lyrics, fear, the devil, hell, the judgement, the afterlife/eternity, temptation, magic, dreams, revenge, marijuana, LSD, DNA, heroin, cocaine, conception, childhood, the past, present and future, death, deception, drug addiction, overdoses, biblical reality, mythology, theology, domination, the horrors of war, poverty, the state of the world, work, politics, disease, medicine, women, children, family breakdown, youth culture, skinheads, violence, paternity suits, nuclear holocaust, pregnancy, rest, peace of mind, libido, unfaithfulness, sorrow, lovelessness, desire, class, armies, witchcraft, brainwashing, mental illness, paranoia, insanity, human nature, boredom, searching for meaning in life, tripping, societal caring, God, Jesus, the Pope, science, religion, comics, revenge, escapism, youth, manipulation, enlightenment, personal change and growth, peer pressure, the choice in salvation, revolution, rebellion, the peace movement, love, Eastern philosophy, transexual confusion, managerial hassles, lonliness, pollution, the environment, suicide, unreality and fantasy, broken relationships, Catholicism, Christianity, Satanism, religious cults, the occult, preachiness, self determination, marital bliss, sexual satisfaction, God's intention in creation, doubt, the disposability of fame, the media, the influence of movies, town planning, colonialism and slavery, recovery from depression, loss of vision/ clouding of judgement, schizophrenia and hope and these were not put across by the music but by the singer. Yet for the most part, it's the music that's remembered.
That's quite an illogical list. The compiler says "This list does
not include persons who frequently share lead vocal
duties with other members of a given music group (e.g.
John Lennon of
the Beatles)" but then goes on to list both Roger Waters and Dave Gilmour of Pink Floyd, while further illogicalizing matters by leaving out Rick Wright. They also leave out George Harrison, either as a Beatle or as a soloist. They leave out Ringo too, but then, it is Wikipaedia !