It's funny now because so many high school pitchers are pitching in the 90mph range (145kph) but back in the 90s it was so unheard of that Goro looks superhuman when he exceeds 140kph (which is still very good for a modern day high school pitcher)
Yeah, in fact, Japan finally reached the 160km/hr checkpoint in competition. Sasaki Roki is a modern-day baseball monster

He actually broke the 100mph barrier during a training camp (with 163km/hr or 101mph) but at koushien, well, pitching at your absolute limit all the time could be dangerous so I assume he's been limiting himself a bit.
Still, yeah, training methods and technique were much more primitive back then. It's awesome what science can let our athletes do.