Hmm.. I've used Mega Pinsir plenty and have never used Earthquake for anything, but Aegislash. And it's hardly thwarted by Earthquake omnipresence, it's still the best mon in OU regardless. Plus, the only reason a bunch of mons are running EQ for coverage is because they're too scared to give Aegislash a free switch in.
What Aegislash seems to be is a power creep cap. It's holding back a lot of "true power" without being broken itself. If many mons didn't have to think about Aegislash, we would see another blatant power creep in OU. However, I don't really see this as anything other than opportunity cost. You CAN go all out and try to use mons that are restricted by aegi, but take care of aegi first. As I've seen in this suspect test so far, his presence holds back OU from being an allout power creep, even more than we saw at the beginning of this gen from megas and priority 120s TF. I see this as a plus. You have the option to run a more destructive set with pinsir to take care of skarmory/rotom-wash. However, you lose aegislash. It's a fair trade in that regard. Really, complaining about that isn't reasonable.