I think it's fine as long as we have a worthy set of people dominating. I agree with what Dallas said and from a ticket-spending spectator's point of view, we want to see quality, and if it's quality that dominates, that's how it should be.
That said it'd be great to see a guy like Raonic or similarly talented new names make it deep and make some noise every now and then, but yeah, it should be that the four top ranked players are consistently the best and it should take a great performance by someone ranked low to reach the deep end of a Masters. And we have had just that kinda thing in the past from guys like Isner, Berdych, Tsonga etc. Those are the kinda players who are good enough to make it through every now and then and they are worthy players. If they made it to the deep end more often they'd be part of this "domination" talk and would have been in the top ranking spots. But they're not, and that's why the rankings makes sense.
Now I am not bringing surfaces into play here for obvious reasons because I also agree with what Shank has to say about surface homogenization. But I like saying "ok here's the tournament, we'll probably see Nadal and Djokovic in the final and maybe Federer and Murray can upset one of them in the semis. And hey, here's this dark horse player who's been on a hot-streak, let's see if he can break through and do some damage here!". And that's fine with me. Maybe it won't be if none of the folks dominating have an interesting game but thankfully, I love to watch at least 3 of the 4 top 4 players any day of the week. And I feel like this is by design, for the most part it takes a lot of skill and talent and hard work all combined to put yourself in the domination equation so there's always something to watch and appreciate. That's the reason why we don't have someone like Gasquet or even "exciting young players" like Gulbis dominating anything despite their supposed talent. Because it takes all that and more to be at the top.