To your point that development is culturally defined I think only applies to some aspects of development. There are also objective aspects of development such as reducing infant mortality rates, disease prevailance, vaccinations, literacy rates etc. I think that these developments forms need to be combined with some subjective harder to define concepts such as rule of law, political freedom, economic freedom etc at no expense to others as Sen writes if we want to see development.
Your second point is very interesting because states are often unwilling or unable to grant "development rights" to their citizens because of the power threat they percieve it brings to them. This raises the question of how can we convince the leaders of these nations that giving citizens more rights is also in the leaders best interests? Well, I think this is possible when we look at the interests instead of the positions that these states have. For example if a states´ position is they do not tolerate political speech freedoms this could be due to an interest in avoiding internal conflict at all costs. The BMZ report shows us that a HRBA where more rights are given can actually avoid conflicts. So there is in fact a differnt and more effective means to the end that the political leaders want.