Like with catcher, this was really a contest between two players. Dick Allen and Mark McGwire.
I'm not offended that McGwire did steroids. I do however think there is a reasonable argument to be made that, had McGwire not taken steroids, he wouldn't be in the Hall of Fame discussion.
If we complete ignore the steroid issue, this is very close.
Allen's career numbers aren't quite as impressive as McGwire's career numbers, but when you adjust for the era he played in, they're close.
McGwire had a career OPS+ of 162, compared to 156 for Dick Allen. Both are in the top-20 all time in that category. In one more season, McGwire was worth about two more WAR.
Dick Allen led the league in OPS four times, McGwire twice. Allen led the league in SLG three times, McGwire four times. Both led in OBP twice.
Allen and McGwire were two of the most powerful hitters ever. Allen was a .300 hitter, but he didn't walk as much as McGwire. Their offensive numbers were fairly close, overall.
Allen played more games at first than anywhere else, but he also played third, and in the outfield. He wasn't a good defender anywhere.
McGwire was probably better at first than Allen. But the fact that Allen could play solid defense elsewhere helps his cause.
Allen, in his best seasons, was probably slightly better. Allen has two 9+ WAR seasons. McGwire's highest WAR was 7.2. In his best season, 1972, Allen led the league in OBP, SLG, OPS, HR, RBI, and BB.
While his raw numbers couldn't touch McGwire in 1998, his OPS+ of 199 was much closer. Allen played solid defense that year, McGwire in '98 did not. Allen stole 19 bases that year, McGwire stole just one.
By all accounts, Dick Allen was kind of a dick. But most of his teammates did not dislike him, and some even considered him a very good teammate.
His attitude issues, in my opinion, color the perception of him. He truly was a great player.
Dick Allen had an up and down career, but at the end of the day, his 1964, '66, and '72 seasons were all MVP-caliber years. His career numbers were probably as good as McGwire's, and his prime was probably better.
McGwire took steroids. If I have a Hall of Fame vote (someday) that's something I do have to consider. Can I say, without a doubt, how much the steroids effected his play in the late 90s? No, I can't. But that's up to the voters to decide.
In my opinion, we can't accept his 1998 season at face value. I think McGwire should probably be in the Hall of Fame. But Dick Allen should be in there first.