Harden would be very similar to Miller in that era, I agree. Reggie had some nice games, but he wasn't a dominating player that no one could stop.
I'm just commenting on the difference in rule sets that have allowed a game like Harden's to become so dominant in the modern era. His game is almost entirely built off the space that the current defensive rule set provides. Literally, almost every patented move of his is created to take advantage of that. Good for him! He's one of the best scorers the game has ever seen, and he arguably has more technical skill with a basketball than any of the old era players. But LMAO at your remark that no one in NBA history could shut down Harden. No one can now, yes, but that's because you can't play defense the same anymore. Harden and contact are like superman and kryptonite. I can promise you James Harden isn't averaging 36pts per game against the 1991 Knicks.
LBJ's game would have translated to the old era. He would have averaged 30+pts vs those style of defenses, just like MJ did. Players like Harden and Steph's game would not have, at least not remotely to the same level. That style of modern player is a manifestation of the scoring-based rule set the league spent two decades working towards.