Generally hard anodised 7075-T6 aluminium sprockets last half as long as good quality steel sprockets. I would suggest that the sort of wear you're experiencing is very definitely abnormal. There is no way even an aluminium sprocket should hook up like that in just 1200 miles; even on a poorly maintained bike or one ridden in sand you'd expect to get more life out of it than that. It must by a duff sprocket or maybe even a fake Renthal of which there are quite a few being leaked on to the market at the moment by unscrupulous ebay sellers.

I take it your chain is OK and not stretched?

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