Ai Servo can be used on stationary subjects BUT not in the usual way you would use AIS, imo.
AIS is predicitve whch means it expects that if something is moving in a certain direction, relative to the camera, it will keep moving in the same direction.
If you are taking a picture of a person and they are changing pose/position/head angle and you are weaving back and forth, side to side, forward backward, the odds are you aren't going to get much in focus shooting wide open in AIS. You still need good technique.
Did you actually try and do a micro adjustment with the camera on AI Servo ? That sounds like it wouldn't work.
There is still the issue of what the camera actually focusses on. It does require making a decision, while in AIS. Sort of like manual focussing, without manual focussing, in terms of the decision process to, when, press the shutter.
With that said, I almost always have the 5D in AIS but lift off the AF when I think I nailed the focus. This for stationary subjects. For events, my camera is used in AIS, the way it was intended and works fine. I woud never get any shots in One Shot.
Under what shooting conditions are you getting OOF shots with the 85L ?
I notice all your other lenses are f4. They, generally will have sufficient DOF to mask poor technique. I had the same problem as you, when I got the 85/1.8 and started shooting tight head shots or head and shoulder shots. I didn;t realize that I actually swayed a bit, between focussing and tripping the shutter.