I study music and voice in college right now, plus I sing jazz and classical, so I am constantly having to think about these things.
Aside from Amy's drinking and drugs, there is a LOT that goes into proper singing technique - even with pop music. Her singing was wonderful, but not technically correct in many ways. Especially when she does a lot of the high passages and runs (especially in "Cupid") in her belt - that is not particularly healthy. The vocal chords are thinner than paper and are very small. I can guarantee that combined with her lack of technique, as well as her drinking and drug usage, she probably had vocal nodules (small blisters and markings that are damaging to the voice).
Another part of it is her posture and how she supports with the breath. She often bent and breathed in ways natural to her, but not healthy. Her posture often doesn't allow her breath to flow properly, causing a lack of support. The proper way to breath is from the diaphragm (located right below the rib-cage), not the shoulders. And a healthy way of supporting your voice is to breath from the diaphragm and keep the air "spinning" (keeping a steady stream of air flowing). Also, constriction in the throat (when it gets tight due to lack of support or uncomfortable ranges) could have also been a problem.
It is hard to tell what exactly about her technique was good and what wasn't without close observation of her, but generally speaking, she did not have (as most pop and musical theatre singers do not) the best musical technique. But, I bet that good technique might have limited her vocal creativity.
However, I do not think her technique was terrible. As a matter of fact, Whitney Houston's technique was AWFUL. Whenever her jaw shook, it was a sign of jaw tension and poor support. Her belting was not healthy and ruined her voice. I think that had she not done drugs, her voice would have still rapidly declined. During her "Bodyguard" tour, she was instructed to cancel her tour because of vocal nodules, but didn't. She got surgery, but that does not fix the problem entirely. Aretha Franklin also has poor technique, which is why her voice has drastically declined over the years. However, look at Patti LaBelle. She belts like crazy just like Aretha, but she can still do it today like she could do 40 years ago - because of good technique.
I can tell you that Mariah Carey's voice is going downhill fast. In general, when women belt, it is NOT healthy. There is healthy belting, but few women know how to do it properly. Mariah belts improperly and her whistle register is suffering, too.
Comparatively to some of these ladies, Amy's technique was not that bad. Part of it was she didn't try to belt as much as these other ladies did.
What are u talking about? Whitney Houston had GREAT technique in her belting, and in her prime, her technique was amazing. She could sing the words so correct and great and her belting was very in comfortable range for her. She could sing so easily, especially in ANY live concert until 1996. Thats how she is known about, slaying every song in live better than in the studio. Whitney's main problem was nodules and drugs which prevented her voice, and made it huskier and more darker. The jaw shooking was because her husband did beat her, and this was not because of her technique. WHitney from 1985-1996 was UNTOUCHABLE, and with AMAZING TECHNIQUE, there was no other female who could reach her singing and technique. Even Mariah. The "bodyguard" tour was about to cancel because of those nodules, but she still got the great technique at that time.
After 1996, Whitney got very heavily into drugs, and alcohol, and her behavior became erratic and she got few incidents from Bobby, he beat her, she smoked (Smoking cause so much destruction to a voice) and Whitney lost BREATHING control. Thats what was the MAIN issue with her. her voice, technique still was there, but breathing was so bad. After 2001 she could barely sing a live song, but the voice and technique was there...
Now, Mariah... Mariah had WONDERFUL technique and voice and belting from 1990 until 1997 and for some reason her live performances started to suck, she started to lip and prerecord vocals. Her head belting note was fading away, and she couldnt sing the way she was used to. there was NOT a chance u could hear Mariah high note after 97 LIVE because she was prerecording the vocals, and lip synching them. But Mariah had also AMAZING voice and technique. But nobody ever know what was REALLY happened with her voice. We will never know...
Whitney 1985-1996 and Mariah 1990-1997 was UNTOUCHABLE forces with their voices and techniques.
The most unhealthy belting i ever heard was Christina Aguilera... God this girl, i dont know how she still got a voice...
Amy Winehouse technique was also AMAZING. But when she was SOBER. At some reason her live performances she got carried away, and this drinking and drugs made her away from the actual singing. Amy could SLAM a song live better from the CD. I compare Amy's to Whitney technique. But unfrtunately, there was a lot of reasons they couldnt show their full potential.