I did do some light testing on the PTR and it does seem like the big culprit ironically is high haste, as that gives you too many Aimed Shots to use if you also want to use Precise shots.
The opener is really weird as you quickly try to dump all your abilities at once so they can go on the cooldown, but after a short time the rotation does actually become somewhat useable, at least in the sense that you feel you can use Precise Shots without wasting Aimed Shots.
Though that being said I am still not sold on whether this is actually what the spec should be. Even if we presuppose not having to use Arcane Shot at all is a reward for optimizing the spec it still feels like ass to ignore the only proc we have. Not to mention that I only really managed to get the rotation somewhat bearable by only choosing the most basic of talents.
So I guess MM is actually not completely broken, though I still feel we deserve better than another expansion of looking at our talent tree and wondering what it would be like to have choices that actually affect how we play the spec, or worse still having a core the rotation and talent choices could supplement.