[Marksman is] still pretty useless since Squad mates are not aggressive like the player.
I'm with Excella Gionne on this.
While I agree with the sentiment that all powers should work correctly on squadmates, I still think Marksman is a terrible talent on Ashley.
I used to spec into it when it used to work, until I realized a few things:
1. Shepard can kill much faster than any squadmate; a byproduct of squadmates dealing only 30% of base weapon damage by default.
2. On Ashley, Marksman has a shorter duration than its cooldown (by default). Squadmates do not fire continuously, and tend to fire in bursts. So not only would Ashley be without Marksman for periods of time while it is cooling down, she would also not be using it while she ducked back into cover every few seconds.
3. Using Marksman locks her out of using Concussive Shot, which is a great combo detonator.
Once I realized all that, I never specced into it again and Ashley became a much more useful squadmate.