A data-driven and thorough analysis by fivethirtyeight makes a compelling case that the balls are indeed juiced
https://fivethirtyeight.com/features/in-mlbs-new-home-run-era-its-the-baseballs-that-are-juicing/
Every time MLB goes through one of these periods where power numbers across the league either boom or bust, it's pretty much a guarantee that they're messing with the baseballs.