I made a list of all the players in history with 300 or more PA and an ISO of .200 or better, which is 298 players, and I ranked them by $HR rate. The top 25 are shown below:
The reason I set the PA threshold so low was to include all the young players just starting their careers, like 2017 Home Run Derby champion Aaron Judge. Counting these short-timers, there are now thirteen players who have hit homeruns on 10% or more of their batted balls, the oldest of whom is Mark McGwire (born 1963). Four of them were contestants in the Derby last night.
The reason I think McGwire took the baseball world by storm in the '90s was that he gave us something no one had ever seen before. There had been a lot of exciting power hitters since Babe Ruth, but none of them had ever equaled or surpassed his 9.9% $HR rate. McGwire, at 12.5%, obliterated that mark (like he obliterated the single-season homerun record). On average, one in every eight pitches he connected with over the course of his career cleared the fences.
Out of the Gen-Xers (known as baseball's Steroid Generation) with 10%+ $HR rates (McGwire, Branyan, Thome, and Dunn), only McGwire was an admitted (or even suspected) PED user. And baseball has adopted strict drug testing since Big Mac retired.
So why are there now NINE Millennials with $HR rates north of 10%? The reason for the surge in homeruns over the last couple seasons may provide the answer. Many people suspect that the balls are now juiced (to make up for the fact that the players no longer are). The table above lends credence to this theory. Of the top seven batters in career $HR rate, six of them began their careers in 2013 or later. The other one is Mark McGwire.
But beyond that, hitters these days are more willing than ever to strike out an exorbitant amount of times in order to hit the ball HARD when they do connect. In a way, they are following Babe Ruth's approach to its logical conclusion.
McGwire still has by far the best $HR rate for players with long (3000 PA) careers, but three very young players have surpassed him, for now. Joey Gallo and Aaron Judge each have $HR rates of .145, meaning better than one in seven of their batted balls leave the yard. Ryan Schimpf, meanwhile, is homering once every eight batted balls, the same rate as McGwire.
But while Gallo and Schimpf (career batting averages of .186 and .195, respectively) haven't made consistent enough contact (or hit safely on enough of the balls they do put in play) to truly be offensive powerhouses, Aaron Judge (career .296 BA) and, to a slightly lesser extent, his teammate Gary Sanchez (.285) have stayed true to the all-or-nothing approach without seeing their batting averages suffer. Whether they can keep it up remains to be seen, but as of now, Judge is beginning to fill the role in the baseball public's mind of the larger-than-life home run hero, more so than any other player has since Mark McGwire.
Being 6-7, 280 doesn't hurt, either.