"but probably not": Actually, probably so. The scholars who favor the indigenous explanation are a small minority outside of India. It's possible it was independent, but very, very doubtful, and none can explain the enormous gap in time between the Indus script and later Brahmic scripts.

What does it matter if some scholars are from outside of India? All I am seeing are conclusions from unstated assumptions that appear to be drawn from a bias.

My conclusions are coming directly from the Wikipedia articles that I linked to. If I am that wrong then edit the Wikipedia articles.