Maybe you assume that random developers will speak up, point out an inconsistency, and everybody agrees to make it consistent from now on. In a small team it might work that way, but "system design" implies a larger community to me. Consensus is hard.

The whole point of responsibility is that blame and praise is focused. A focus on everyone is no focus at all.

Well, we do have traffic police and courts and lawyers.

Yes, everyone should follow the rules. But the point of having an individual responsible for conceptual integrity does not mean, no one else should care and do whatever they want, but that there is, if needed, "police and judges" in place...

But there is another point: the fewer people the easier it is to have a consensus about what the conceptual integrity entails. If you have a single judge, you are more likely to expect consistent rulings, so to speak.