Alan Greene is mostly accurate in that one’s vocal practice does little good until the tension is gone. He’s saying that the practice can develop bad habits.
This is somewhat accurate–that tension causes other types of sounds to emerge. And because hearing remains inaccurate with bad posture; such that, due to Maya and even accompanying music, one continues to believe that one is singing accurately.
However, this Vocalposture’s detensing involves the entire body and can take a very long time. Also, the optimal goal is flexibility to tonal and body changes, such that the practices can easily change to a new style, due to detensed tissues.
Hence, Vocalposture’s methods differ from Greene in that vocal exercises start early, before all tension disappears. Vocalposture is concerned about excessive tensions that may injure voice, so harmful singing should not be part of its initial exercises.