Right. I wouldn't put anybody on the Celtics in the top 20. However, I think ESPN was correct in putting all of the Big 4 in the top 40.
Even if you don't particularly like Rondo or Pierce, if you include defense as well as everything else there aren't 20 players better than KG.
I'm a big fan of Pierce and Rondo. I include defense as well as everything else, but it isn't everything. Indeed, it's only half the game, and while KG's tangible and intangible effects on a defense are very valuable, in a vacuum I'm comfortable saying that there are 20 players in the league right now who are more valuable on a night to night basis.
Put a different way, on a team already filled with highly talented players (particularly scorers), KG is a lot more valuable than a guy like, say, LaMarcus Aldridge or Kevin Love. If you're picking building blocks for your team (#1, #2, #3), however, KG is significantly less valuable than those guys. He's much more complimentary than foundational at this point, and in my opinion should be ranked lower.
Rondo is on the cusp of the top 20 for me, but his well documented and much discussed / argued about weaknesses on the offensive end and his maddening inconsistency (even on defense) place him behind guys who are capable of carrying their team on a nightly basis. Again, with Rondo I think it's a matter of him being extremely valuable in the right situation, but having a smaller individual, dominant impact in a vacuum when you're looking at his individual skills.
As for Pierce, I think he's a very solid overall player, but his game and athleticism have dropped off enough that he's outside the top 20 at this point. He's still top 5 at his position, but only just. A major factor that I take into consideration with Pierce, as I do with KG and Ray, is that while they are very good players, they aren't capable of sustaining a very high level of play for more than 30 minutes or so a night. We've seen the last couple of years how they often run out of gas. That has to factor into their ranking as well.