A very interesting video and transcript. Sai's summary from the end (though of course it's just a summary, and the analysis is elsewhere in the transcript and in Sai's articles on the subject):

I think the founders wanted to create a strong executive—not all-powerful, but strong.

And they wanted someone in charge of law execution. I think that's the principal function of the executive, not rulemaking and not acting as a substitute court.

And they had examples of plural executives in the states, and they eschewed them.

So I think the Court got it right….

I … think the country is better off having a president in charge of law execution rather than having a bunch of people independently doing it.

Having said that, we do have states where we have plural executives, and it's not as if people think they're dysfunctional.

But I think there are advantages to executive unity, particularly when it comes to law execution.