Yes, big league hitters have to guess. I played in college. I played against a ton of guys who got drafted and even against a few future major leaguers. Here’s the deal about speeds. When I played 20 years back, if you threw 90 in HS, you were getting drafted. Hitting a 90mph pitch wasn’t that hard. You had an extra split second to see it, track it, and get your hands to it. 93-95 was an order of magnitude more difficult to hit. It’s only 3-5mph but your eyes see it as 50% faster. It’s strange. Hardest I ever faced was 98. I never saw the ball path. I heard it and I saw glimpses of the pitch as if I was watching the ball come in on an old movie reel. There was release, then halfway then glove. My eyes and brain couldn’t process it until it was in the glove. So you guess, adjust location and go. Made good contact, but if he threw an off speed pitch, I was meat. 95+ was rare 20 years ago. Now 95+ is the expectation. That’s insane
Also, while raw strength isn’t sapped into your thirties, quickness is. Bat speed is not about raw strength. It’s about quick hands. That’s why you don’t see a ton of enormously jacked baseball players. They’re typically long, slender and flexible with strong as hell hands.