I'm a little over 3 years in from a grade 3. 63 years young. Did some physio at first but not for too long.
2 years later I tore the rotator cuff, same shoulder. Brutal but currently manageable.
Get some serious aching sometimes but most of the time it's good. Doesn't hinder the riding.
Remember that these ac separations are complete tears of the ligaments and there's no healing from that.
The best thing you can do is keep working on muscle strength in the area.
I was advised that surgery for the ac separation is many times worse than the original injury and outcomes are commonly not positive.
Got the same advice for the rotator cuff and things are working pretty good for the moment.
Good Luck and hope it gets better.