Robinson was not a good playoff performer for a player on that level. Saying Robinson was a pretty good playoff performer is just inaccurate.
You make a very good case against Robinson but I think you are leaving out a big part of his impact. Do you have any indications that his DEFENSE dropped as well? It's half of the game and for David Robinson, more than any of the others on your list, it's the bigger half of his impact. I hadn't read trex's post yet, he brought up the same point.
I did notice that Erving went up the most on your list, I am a bit surprised, I would have guessed Barkley.
Also interested to see if any analysis done to see if a guy like Barkley, known for not putting in consistent effort or focus on his defense, was harder working and more focused defensively in the playoffs. I know that players like Jordan and Kobe were more focused defensively in the playoffs from watching them but I don't remember enough of Barkley's effort there to trust my eye test v. what I saw from his regularly. If someone can show me that he played defense at the level he was capable of rather than continuing to dial it in, he moved from someone who is probably in the 30-50 range for me to someone who would be considered here in the 15-25 range which is a big jump.
I remember running some numbers about how well Nash's offense and Ewing's defense translated to postseason performances as Rtg numbers. (They were pretty much on par with each other)
When I did that, I was also curious about Robinson's defense and even though right now I don't have the numbers (I don't keep worksheets), I remember the defenses Robinson led were not on par with Ewing's led defense numbers. But I didn't take it as a direct knock on Robinson. Rather, it made me move Ewing up on my goat defenders list. Though, that situation created a direct gap between Robinson and Olajuwon/Duncan.
Also, it's worth noting that Robinson did not have a coach like Pat Riley to dictate such effective defense. So, Ewing's numbers did not make up for the entire gap between him and Robinson.
[I decided to run the numbers again to see if I'm mistaken but I guess not. This part is like an edit in advance.
Ran the numbers again to see how well Robinson led teams performed on defense in the playoffs.
From 1990 to 1996, it was -2.6 rDRtg for the Spurs.
With excluding the best and the worst to see more about distribution; it was -1.8 rDRtg. (The best; -11.2 rDRtg against the Lakers in '95, the worst +2.0 against the Jazz in '94.)
Not that great. It's good. But not particularly great or historically great.]
The code in the spoiler has the numbers I ran if someone is curious about it;
Defense is half of the game. Sure. I don't deny anything about that. But Robinson was not Russell.
Anyone that made the list other than Russell and Garnett, are also better offensive centrepieces than Robinson. And if you saw my arguments, I was also against Garnett being that high on the list. I argued against him as well.
Robinson's defense yielded goat level defensive results in playoffs when he did not have to carry his team's scoring / offense.
Going back to postseason resilience on offense; it is the thing what puts a team over the hump.
I mean haven't we seen enough of Harden in recent years to know that if your team designed by scoring XX amount but you can't match that in the playoffs?
And we're yet to run out of those guys.
As for Barkley's situation
This is the criterias I go by;
Peak (single season peak and extended peak as two or three seasons peak)
Average prime level
The main thing about Barkley will be prime duration and intangibles for me. Due to his laziness, his prime lasted shorter than it should and that's also an intangible issue obviously. I'd probably have Barkley over Robinson though. I'd take Barkley's offense over Robinson's defense. The level change from regular season to playoffs in Barkley's defense and Robinson's offense, I'd go with Barkley. Though we could argue over Barkley's elevated defensive level not matching Robinson's dropped offensive level, but the gap between Barkley's offense and Robinson's defense is more significant to me. Barkley's shorter prime is not an issue against Robinson.