I remember reading something that disproved your point b): mixing students from different socioeconomic background (which in general is a very good proxy for ac

I remember reading something that disproved your point b): mixing students from different socioeconomic background (which in general is a very good proxy for academic performance) benefited the poorer students a lot and hardly had any impact on the richer ones. So in short taking out the best students of a diverse class only negatively impacts the ones who stay. I can try and find the exact reference, but a quick google search brings up a ton of articles on socioeconomic mixing.