So the conclusion is that anytime a character is not using deadly strike, he is giving up a significant portion of his damage ability. As currently written, I think this maneuver is likely too powerful. It's simply too swingy in damage between when its used and when its not, and it creates too much competition for other maneuvers.
I would say though... that I think it's actually good that DS is the top of the chain overall across the board. Because one, it means that every Fighter has the best maneuver there is (so that if nothing else... every Fighter is equally balanced at max efficiency). And two... it allows you to have maneuvers which situationally are more effective than DS if the circumstances are right. We don't want them universally better as often as DS is (because that just overpowers the Style), but its cool when a Maneuver has a specific time or circumstance where they can potentially just blow DS out of the water. Because then it becomes a tactical decision when to use it.
The hardest part is figuring out realistically how often some circumstance will actually come up, and whether the bonus you get for when it does is proportional to that. So for example... your comment on Opportunist is right on the money about it not occurring enough to make the Maneuver viable compared to others... which means you either need to up the power of the Maneuver even higher so that someone is willing to wait long periods of time for the circumstances to arise to use it (and then can go ballistic with the maneuver at that time)... or increase the amount of circumstances the Maneuver can be used (thereby keeping the power lower).
Perfect example is Sneak Attack. It's finding the balance between how often it can be used versus the power of it when it finally is. Should it do more damage than DS when it can finally be used... if there are many barriers put up to do so? Should the fact that the Rogue shouldn't be more powerful than a Fighter in a fight change the balance between effectiveness and circumstance? These are questions that need to be answered to make sure all the Maneuvers end up being useful to somebody at some point.