Bitcoin and altcoins are heavily correlated, we all know that but they do not move at exactly the same speed and we can clearly see this is the case, at the beginning of this bull run most of the growth was concentrated on bitcoin and that is why its dominance was going up almost everyday.
Now we are seeing the opposite with altcoins growing faster than bitcoin and taking away some of the dominance of bitcoin, so even if both altcoins and bitcoin move on roughly the same direction the rate at which they do is different and that can be enough to produce profits with the right strategy.
But I'm not sure what kind of strategy will be useful here when bitcoin and altcoins are moving on the same direction but at different rate. Because what I am trying to say here is, instead of focusing on bitcoin dominance as a bigger thing here for decision making, we can go for fundamental and technical analysis on altcoins to predict its direction; that will be much easier than get confusing about bitcoin dominance as a tool to predict the movements of altcoins.
As far as my experience concerned, there cannot any single rule which will be demonstrating how bitcoin dominance is influencing the movements of bitcoin and altoins and how affects each other. So, focusing on other strategy will be helpful and less confusing.