That's the nature of a progressive tax system. If you give relief to the people at the low end, the people paying more get it too.
Oh I realise that but you can counteract it by adjusting the top rate.
Its the people at the top you need to keep, and their skills make them the most transportable world wide.
10% of NZ registered nurses now work in Australia.
Those that do better in life is inevitable, however they are not an infinitely exploitable resource.