He was no weakling, but he was definitely a line-drive hitter. He’d probably have a hard time reaching the upper deck in most ballparks — not because he wasn’t strong enough to get a ball there, but because he wasn’t known for hitting towering fly balls.
The ball he hit at the Polo Grounds traveled an estimated 470 feet. That’s a pretty good shot. But yes, he was more of a line-drive hitter. He decided to try for more homers after setting a record for winning the most consecutive times (six) in the tv show, The Home Run Derby.