Although I give Barkley the advantage as the superior offensive player, his playoffs production doesn't really surpass Duncan in any metric, offensively, tbh, even if we ignore totals..
Prime and slightly past prime Barkley's playoff Rebound % is 18.9, while Duncan(using the same criteria) has a rate of 18.7..
Assists is Barkley at 18.3%, and Duncan at 18.9%..
Using PER and WS to summarize the box score numbers(which is essentially what the OP is doing, using simple box score numbers), Barkley posted a total 25.3 PER and 0.201 WS/48, while Duncan posted a 25.6 PER and 0.214 WS/48..
So, offensively, their playoff output is virtually the same, once you adjust for pace, as shown by these numbers..defensively, as pulp already pointed out, the difference is the disparity between Marc Gasol and David Lee, tbh..
If you want to include Karl Malone, it's even easier to roast, since Malone had a reputation of choking in the playoffs, similar to David Robinson, tbh..
OP used arbitrary, cherry-picked numbers to form an argument..once you expand the discussion to include actual evidence and facts, Duncan blows Barkley and Malone out of the water..as for Hakeem and Shaq, I'd have Duncan below both in terms of peak play, but ahead of them from a career perspective..