I mix historical players with the current so I can have Mike Trout face Lefty Grove and the like. By in large, the HoFers I import tend to be among the best players in the league. However, if you use the OOTP development engine, their career arcs may be different from RL which is to say their time of peak performance may be shorter than what it was in real life. But, in some cases, they stay among the best in the league longer than they did in Real Life.
Right now, Christy Mathewson is the ranked as the best pitcher in my league. The AI was smart enough to make him the #1 overall pick in the Inaugural Draft. I'm six seasons in. He's won exactly 20 games twice, the other seasons he was in the high teens. His career ERA as of the moment is 2.38. Those numbers are not as good as what he actually did because the league is using modern total modifiers, so pitchers don't go 300+ innings and no one wins 30 games. However, in Real Life he struck out 4.7 batters per 9 innings. In my universe he's averaging 9.7. Different era, so he's out performing in that metric. So his performance in a modern era is still among the best compared to the other starting pitchers, but because it's a different era the actual numbers will not match what he did in his real career.
To give you an idea, among position players right now Francisco Lindor is ranked right ahead of Ken Griffey jr. and Honus Wagner is right ahead of Bryce Harper. To give you an idea
