This is a decent list (and much better write-ups) - worth reading through if you are interested in basketball history:
https://forums.realgm.com/boards/vie....php?t=2012241
I don't think the list is *that* accurate so take this with a grain of salt but it certainly supports the idea that Lebron faced much tougher competition in the playoffs, especially when both had legit title chances.
MJ played 4 top 100 teams in his 6 Finals runs and none of them in the top 60.
64. 1997 Jazz (won)
74. 1992 Blazers (won)
75. 1996 SuperSonics (won)
100. 1991 Lakers (won)
Lebron played 9 top 100 teams in his 10 Finals runs, all of them in the top 60 and 4 of them, top-9.
1. 2017 Warriors (lost)
5. 2018 Warriors (lost)
7. 2014 Spurs (lost)
9. 2015 Warriors (lost)
21. 2013 Spurs (won)
26. 2016 Warriors (won)
27. 2007 Spurs (lost)
41. 2011 Mavericks (lost)
56. 2012 Thunder (won)
Somehow all of those 13 top-100 teams they faced were in the Finals. And this means 9 of Lebron's 10 opponents in the Finals are ranked higher than any team MJ faced during his championship runs. That is nuts.
Outside of these Finals runs, MJ played 4 top-100 teams:
6. 1986 Celtics (lost)
28. 1989 Pistons (lost)
60. 1990 Pistons (lost)
97. 1988 Pistons (lost)
Outside of these Finals runs, Lebron played 3 top-100 teams:
54. 2008 Celtics (lost)
90. 2010 Celtics (lost)
92. 2009 Magic (lost)
Playoff series record by team tier (as of 2020, since 2021 teams aren't ranked yet):
Against top 10: Lebron: 0-4, MJ, 0-1
Against next 40: Lebron: 2-2, MJ: 0-1
Against next 50: Lebron: 1-3, MJ: 4-2
Against teams outside of top 100: Lebron: 36-1, MJ: 27-3
Restricting to seasons where they had legitimate championship equity, as in, they either had or would've had a significant chance of winning it all if they got luckier with who they got to face (MJ: 89-93, 95-98, Lebron: 07-18, 20):
Against top 10: Lebron: 0-4, MJ, 0-0
Against next 40: Lebron: 2-2, MJ: 0-1
Against next 50: Lebron: 1-3, MJ: 4-1
Against teams outside of top 100: Lebron: 34-0, MJ: 27-1