Great players somehow find themselves in such situations. By the "how could you possibly know" logic, hundreds of players could be great leaders and HOFers. How many games were the Thunder expected to win last year? Yet Westbrook carried them. There's a reason Carmelo post-Karl has not been considered a great player
Westbrook is in a unique situation, because his body and skillset allows him to do everything on the court. It's pretty much the same with Lebron. Those guys are guards/wings able to ultimately do everything needed for their team to win by themselves. While DMC tried to evolve in such a way, taking his game away from the basket and becoming more of a playmaker, than a traditional big man, he is still a 6'11 guy with a heavy body. Being the player that he is, Cousins relies on other teammates to get him involved more than Westbrook or Lebron and he relies on his teammates to defend the perimeter in a time, where most of the offense starts at the 3pt line.
This has nothing to do with figleafs like character, being a leader or other things that sound great in a discussion between fans, who still don't know a thing about them, because they aren't in the lockerroom and simply can't know, who is a leader, who has a great character, who is a beloved teammate and who is not. It's just that Cousins doesn't have Lebrons or Westbrooks physical profile.
That's why arguments like "Oh Lebron brought a terrible team to the finals. Therefore Cousins is bad, because he can't get his terrible team into the playoffs" are pretty simplistic.
Cousins isn't the player Westbrook or Lebron are. I agree. Well he shares this boat with people like Steph Curry, Klay Thompson, James Harden (although offensively this dude is close), Anthony Davis, Blake Griffin and pretty much everyone in the basketball HOF out of a very select few.
Even worse - in todays NBA getting a team into the playoffs as the main cog, is much much harder as a big man.
1. The way the game is called gives smaller, quicker guys the advantage
2. Carrying a team out of the low post is very difficult, because of zone defense
3. the constant diet of high pick&rolls turns big man, who can't move their feet quick enough, into a defensive weak spot for their team
Still that's doesn't mean, that Cousins can't be successful, when a team is built to his very specific needs. It's honestly not that hard. 1 solid PG and 3 interchangeable, long guys, who play good D, are athletic and can shoot. One of them should be able to run a good pick&roll. And some of them should be able to make good entry passes. That's it. Big deal huh? In all the years of DMC as a King it was too much to ask for a roster like this?