That makes for a good stat discussion. So if Aquino moved to a division where the other teams don't run stupidly, he loses the opportunity to get those assists, so is he actually worth those runs saved or not? I guess when you have a player ranking that depends on what other players do or don't do to allow you to make a play (and I suppose all defensive stats have some of that character, though some more than others) that's one more reason to stick with larger aggregates when trying to evaluate players from defensive stats. It's the same old old story about great RFs. When they come into the league they rack up a bunch of assists and then their assists drop. Of course that has two possible interpretations 1) they lost their arm 2) guys stopped trying to run on them. You might have to dig a little deeper to find out which!
I suppose you can even make the same argument for hitting stats since divisional play means different hitters to see a different cross-section of pitchers, but it's generally assumed all hitters see a similar enough quality of pitching over the course of the year that stats are comparable, though I wouldn't be surprised if there have been cases of divisions with differences in overall pitching quality that did reach statistical significance.