So far this year, the AL is averaging 4.41 runs per game with an AVG-OBP-SLG of .257-.322-.405 and an OPS of .727. 1992 was the last year the AL had a lower runs per game with 4.32. Same for OPS, .713. Last year the AL R/G and OPS were 4.45 and .734. So not too big of a drop off. Of course, things can change with Sept.
So far this year, the NL is averaging 4.15 runs per game with an AVG-OBP-SLG of .253-.319-.392 and an OPS of .710. The last time the NL had a runs per game lower was in 1992 at 3.88. That was also the last time they had a lower OPS, at .684. Last year the NL R/G and OPS were 4.33 and .723.
The table below shows how each league has done, month-by-month, this year. April includes March data. Both leagues had their best power month measured by SLG and ISO.