One of the biggest advantages of Legacy movement is that Auto Face Target doesn't make you move in bad directions, so Legacy has no reason to keep Auto Face Target off. If you turn Auto Face Target on, you will track enemy movement while stationary without pressing anything at all.
Just tap the Move Back button. The cast part, not really an issue, as casting requires you to keep facing the target until the point-of-no-return on your cast bar anyway, regardless of movement type.