Steph being the most important piece, including when KD was there, is a no-brainer.
Most plays rely on either Steph shooting himself, he posing the danger due to his abilities or his movement without the ball.
It still does not lead to there being one "bus driver" and everyone else being a passenger, that metaphor does not work.
Steph missing is worse than everyone else missing, but Steph still ain´t winning championships without Klay and Draymond.
On the defensive end Dray and Klay are more relevant than Steph and so forth.
Steph being underrated in almost every sense, i already stated that myself, it still does validate Chuck´s metaphor.
Everything else you mentioned has nothing to do with the point i made.
The point is Barkley is not wrong, you're actually oversimplifying it if anything. Ofcourse basketball is a team sport, no one is playing 1v5 out there, but the point is there is usually 1 player who above all else is make or break for the team, the player which the entire system revolves around, the player which is the focus of opposing defenses, and this is what Barkley was referring to.
Durant was doing layup drills out there during those finals.
He was effectively a role player, an all time great one, but he was simply asked to replace Harrison Barnes, and if KD is getting Harrison Barnes level of attention the outcome was inevitable. Both stats and the eye test back this. KD is too great of a player to be treated like a role player, and that's what he was. You're looking too deep into the semantics of the term "Bus Driver" vs the actual point Barkley was making. It's different when you're the head honcho that defensives are primarily targeting, and we know this because KD has never seen the same success before or after GSW. He's folded multiple times when defenses can lock in on him, this isn't something new.