I mainly agree with all you say - but think that the media and the way corporations have constructed society are more to blame than you suggest. Our body images, our attitudes of envy and coveting material 'stuff', tends to arise from images we are being shown continually - in magazines on TV, films etc. Many of these images are constructed and don't actually exist - they only serve the consumerist system we are living within.
I'm lucky to have a good job, feeling 'in charge' and working at something I believe in. I do not seek much material stuff - as I am blessed with great friendships - and we share the wisdom that what is truly important in life is being happy with your lot - not acquisitiveness - or the latest iPhone - but sharing good times and giving / receiving love.
Of course not everyone has the chance to work in a Worker Co-operative - share in a non hierarchical system where one can feel valued and respected. I was lucky to meet some like-minded people four decades ago - that still understand the true meaning of friendship & love. But simple things like meditation on what is truly important in one's life and being grateful for it, can bring a huge amount of bliss into one's life - and rejecting the insistent advertising which tries to tell you that you are not pretty / good / rich enough - or that your life would be complete with a boob job/ pay rise / curved TV is the first step IMO.
I think that ambition to better oneself - and curiosity are inherently human - but that these traits are substantively different to any innate dissatisfaction with ones situation. The feeling that somehow one has the right to expect to 'keep up with your neighbours' and if only you married better / worked harder / upgraded your internet package - you could achieve 'happiness' is simply a convenient way to keep people working longer & harder hours for a 1% that have huge off-shore bank accounts. Happiness is never things - it is internal - being at peace with oneself.
Thanks for the excellent post - it's a really important topic that concerns us all. Peace.
RE: Why Are Humans Never Content