It doesn't seem as if the Miami Marlins are as respected as the team should by the industry. The Fish have more potential than expected, and it could lead to an interesting Trade Deadline down the line. In the meantime, The Fish are still trying to stay competitive, and succeeding at it. The team has an 8-7 W-L record right now and sits in third place in the NL East.
How does the Miami Marlins run differential look like?
It's useful to look at other teams as well, to compare their performance to that of the Miami Marlins. At this time, the team did give up more runs than scored. 65 runs scored and 71 given up led to a 7-8 Pythagorean W-L record. Looking at the rest of the division, the New York Mets match their 10-5 record with their Pythagorean version. They scored 61 runs and allowed 41.
The Philadelphia Phillies are at 9-7 right now, but have an 8-7 Pythagorean W-L record. This is due to them having scored 60 runs and giving up 53. The Atlanta Braves should be better than their 4-11 W-L record. Their Pythagorean record is 6-9, with 49 runs scored and 65 runs given up. The Washington Nationals are at 6-9, but should be at 7-8 according to their Pythagorean record. They scored 70 runs and given up 80.
Looking at some other National League teams, the Los Angeles Dodgers have an 11-6 record and a surprising 9-9 Pythagorean record, due to them surprisingly scoring and giving up the same 74 runs. The San Diego Padres are at 13-3, but "should" be at 12-4 as they gave up 43 runs, but scored 73 runs. The San Francisco Giants scored 75 runs and given up 52 runs. Their record is 11-4, but they should be at 10-5.
I expect the Miami Marlins to at least stay around .500 going forward. It's not a bad team and at full health could even be a slightly above .500 team. Things are finally looking up for the team at this point. I expect the run differential to improve.