Is he doing well at Basis? If he doesn’t mind the rigor and is getting good grades, if he has friends, etc chances are Basis is going to be similar if not better outcomes for graduation and college options. Assuming you aren’t living in Foxhall/Palisades/Georgetown/AU/Cleveland Park/Tenleytown, I bet Basis is also a better commute for him as it’s in the middle of the city next to a Metro.
If he wants a more typical high school experience (bigger building, better sports offerings, more kids for finding friend group, less accelerated program but still access to some Advanced Placement etc) AND the commute to the far west of DC isn’t an issue, then that may be the reason to move. If he is succeeding at Basis I am sure he will do well at McArthur and may even have more options like the academies. If he’s not getting great grades at Basis he may do better at MacArthur and that would probably help his college options.
Good luck!