This has always been debated, because even Carius, Wittmann and Knispel each scored at least 1/4 of their total as a gunner. And what happens in the situation of Bobby Woll, who scored nearly 100 kills as Wittmann's gunner, and then went on to 80 of his own as a commander? Do the kills belong to Wittmann or to Woll? If you give them to Woll, like was done in the case of Carius and Knispel, he is easily the highest scoring commander, surpassing Carius and Knispel. But since Wittmann was an important propaganda tool, it wouldn't do to go giving his kills to his gunner, now would it? Even when it was his gunner whose deadly accuracy and quick thinking had saved the whole crew dozens of times?
I think the question to answer is, to whom is the entire crew's success due?
An example: In the case of Wittmann's expliots at Villers-Bocage, the credit should all go to Bobby Woll, whose fire-on-the-move skills are what enabled the lone Tiger to successfully rout the British 7th Armored. Wittmann was a fairly accurate gunner but could not hit anything while his tank was moving. With a different gunner, the skirmish would probably have had a different outcome.
So I think if you answer that question, the problem will be solved. And in most cases, like Barkmann, even as a gunner the ace-to-be was probably the strong point of his crew.
(I am not sure he wasn't the commander of his Panther at Kursk, because he is recorded as ordering the platoon to weld buckets over their intakes, not something a lowly gunner would do)