Well I agree with your career catagories , roughly, and think it a worthy debate, as most debates that originate at Bettys tend to be, I do take some issue with a few of your points . I would have to say questioning the merit of earlier works simply because there later work is bollocks is , well, simply bollocks. Steve Wonder put out at least 5 great albums in the early seventis and another 4 or so good albums in the sixties over a span of 10 years, Rod put out about 8 very good discs over about 6 years ( including work w Jeff Beck and also Faces, ) MIles Davis , well you did qualify he might be safe from this. I realise your argument was more that these artists did have there quality drop off and I agree there is no doubt about that. Pop music sets the worst example here , think Paul McCartney , The Band, the list goes on and on and the greater the musician the greater the perceived crime. Classical music fares considerable better , but most of them died from venereal diseases ( tut tut) and that moves them into another category, although few doubt Beethovens late years and many more like him.
I think pop music which is born of a non schooled youth , non intellectually rigoris roots has less to fall back on. Thes people are mere babes , who get thrust into the media limelight and treated in a manner which would cause damage to most. It is, I think, the norm- to loose touch with the reality (which early work of pop musicians descibes so beautifully) when you live in such a rarified sterile existent of brown nosing false friends catering to your every whim. Only a massively fucked up person ( Dylan, Coltrane, Neil) or a massively strong person ( Mic Jaggers, Tony Bennet) can servive this and still produce great work. Others rest on the money and laurels and so be it.
I am rambling now , but I think it pointless to dismiss early great work simply because they can no longer pull it out of themselves anymore. As far as the one trick ponys , I think that is simply another category of humanity, and the artists who maintain a group dynamic ( Led Zeppelin, Stones, the who, U2 , have a better chance as they feed of the artistic impulses of others rather then just having producers tell you that the dreck you just recorded is bliss.
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