I'm no physicist but it doesn't seem that it would be that difficult to determine whether the balls are juiced. It would seem that there must be a formula that would include exit speed and launch angle to determine the path and therefore the distance a ball is traveling.
Simply take the exit speed, launch angle, and distance the ball has traveled in the past several years, compare it to the same data for 2019, and voila! Either the ball is traveling farther or it's not and all this speculation about juiced balls is settled!
Of course Manfred has all but said that the balls are juiced this year so that might be proving what everyone already knows.
My belief is that the 2019 balls are stitched tighter and have lower threads than balls of the past, which was probably done to increase the flight of the ball by lessening the wind resistance on the ball. A side effect has been that because the threads are loweer the pitchers can no longer grip the ball as well so the breaking balls don't break as much as the ones they threw in the past (hear that, Rich Porcello? It's not your fault!) which makes the balls easier to hit.
But that's just my theory which will probably be disproven by someone posting anecdotal evidence by noontime tomorrow.