It works on sliding scales. Barkley does not have any job allocated to him to defend. That's the way the system is tactically set up.
If you have a problem with that, look at the manager, not the player playing to instruction.
As said, if we played a different system, then perhaps Barkley would be required to defend and would then deserve criticism. As we don't, he doesn't, so he shouldn't.
Using that analogy again, if the electrician had nothing to do, that would mean the management of the job was at fault, wouldn't it?