He only moved into the part-time role in the past few years. Before then he was the legit CTO of the company.

I don't doubt he speaks like an engineer because is basically is THE uber-engineer. He should be treated more as an oracle than an engineer. There aren't many people I would say that about in the world of computing, but Carmack definitely is that.

This is true. I think a good test for this is that the person making the criticisms also provides alternatives that are reasonable and it's evident that they're trying to make things better and not just arguing for argument's sake.