I think this is slightly specific to astrophysics and cosmology. In Neuroscience, it definitely feels like there is plenty of headway to be made by individuals

I think this is slightly specific to astrophysics and cosmology. In Neuroscience, it definitely feels like there is plenty of headway to be made by individuals with good ideas, although I admit that it feels as though ideas are harder to come by as more is published and the bar is continually raised.