I didn't say the trajectory changed, I said that the trajectory not matching the "actual" speed of the ball is what visually confuses the hitter, making you swing early.
When judging a known object in the air, your brain uses its trajectory to estimate the speed.
I'll bet most of you swing early when you're sitting on fastballs, just like I do.
Especially if you're new to the game, eventually you'll adapt and adjust to the different gravity.