They are a good team, but they aren't as good as their record indicates. They have been fairly lucky as well.
1. Pythagorean W-L, or more simply, average runs scored vs average runs allowed accounts for between 91% and 94% of the variance in actual W-L record. To be 6 games above what the Pythagorean record says you should be indicates some luck. The vast majority of teams will end up within 2 wins of their Pythagorean record.
2. Do you know how difficult it is to sustain a 17-5 (.773) record in one run games? So difficult, that if the Rangers maintain that, I believe it would be the best record since 1901. Don't quote me on that since I'm working off my memory here, but I know it would be close. Most teams, good or bad, will finish near .500 in one run games. The Rangers are currently 6 games better in one run games than .500 (exactly the # of games they're beating their Pythagorean W-L by).
Believe it or not, the outcome of one run games has more to do with randomness than it does with skill. The Rangers have been lucky in that regard.