Mildots are not obsolete. They were designed to be used in applications where shots had to hit center body mass at ranges inside 1000 yards for the most part. They will still do that all day long. However, there are newer systems (which borrow greatly from the general idea of the mildot reticle) that are more precise.
If I needed a "sniper" rifle, and I could pick up a .308 bolt gun with a high quality fixed 10X scope with a mildot reticle, I would feel pretty confident that I could hit center of bad guy out to seven or eight hundred yards all day long.