It's silly to compare the three most recent record holders to Babe Ruth in terms of how much better they were compared to the other players in the league that season. Ruth is way ahead. But it makes sense to compare them to each other.
Roger Maris 1961 61 2.81 (base) expansion year
Mark McGwire 1998 70 3.86 (37.3%) expansion year; 1993 was also an expansion year
Barry Bonds 2001 73 3.67 (30.4%)
Bonds is 30.4% ahead of Maris and McGwire is 37.3% ahead of Maris. I'm guessing that no amount of chemicals could reasonably be expected to explain that.
In 1961 the American League (AL) expanded from 8 to 10 teams, a 25 percent dilution factor. Unlike future expansions, all players were taken from the existing AL teams, but not from the National League (NL). So most, but not all, of the talent dilution probably occurred in the AL. That could have been a big help to the top AL HR hitters in 1961.
Maris had these advantages in 1961 over conditions just one year earlier:
1. weaker pitching
2. 5.2% more games; because of that and relatively few walks, Maris had 50 more at bats that Ruth in 1927
3. Mickey Mantle batted behind Maris most of the time in 1961, although not for HR 60 & 61, both of which were hit in those extra games at the end of the season.
On the other hand, in 1960 with Mantle batting behind Maris only at the end of the season and in the World Series, Maris through the Yankees first 100 games had 35 HR and was on pace to hit about 55 in the AL's final 154 game regular season. However, Maris was injured and finished with 39, one fewer than Mantle who led the AL for the fourth and final time. A reasonable guess is that had 1961 had those same conditions that Maris might have hit about 58 HR but not break the record. I'll take a close look at the top six AL HR hitters in 1961 in a future post.