> As long as other satellites keep being launched into higher but not geosync orbits doesn't that provide a steady supply of junk to navigate around?
Sort of.
1. Modern satellites don't really shed junk - and almost all satellites today have to be launched with a plan to make sure that they deorbit in a timely manner. Doesn't always work out, but most are pretty safe.
2. For space junk, the time to deorbit increases super-linearly with orbital height. Which means that you are correct - stuff in higher orbits will slowly "fall" through the Starlink orbits on their way to Earth. But it's a very slow process which means there's really only a thin trickle of stuff falling from above.
What that means is that, Starlink will always have to avoid objects. But the bulk of the problem, which was caused by this[1] Russian anti-satellite missile strike will go away after a decade or so.
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1. https://www.bbc.com/news/science-environment-59299101
