I think this is an extremely important arc to remember, especially these moments, for a number of reasons. It's a really clear indication of how well Sanzo understands Kougaiji, despite them being enemies. It's part of who Sanzo is to read the people that matter, and he's an extremely empathetic (though not exactly sympathetic) person. Which is a quality needed of a Sanzo. Even Yaone and Doku, who both definitely know Kou a lot better and for much longer than Sanzo has, say "You're right," when Sanzo tells /them/ they're being stupid. "Your boss wouldn't want that." There's an understanding there that I think goes a bit beyond the usual Sanzo understanding.
The biggest thing that still stands out to me from all of this is that despite what he was saying, Sanzo was essentially telling Dokugakuji and Yaone how to save Kou. And he gave them ample time to do it, though he probably could have dealt a more serious blow to Kougaiji (with the help of the others) by the time they turned around. He didn't have to help them decide, but he did.
And then Kou's "looks like I owe you guys again" could very well be directed at the Sanzo party, and you can't convince me it isn't. Because without Sanzo, he'd still be brainwashed, or /dead/. And I think he knows it. He didn't forget anything that happened while he was brainwashed, and Kou obviously would have seen him talking to Dokugakuji and Yaone. I'm sure he's more than aware of what just happened.
Like I mentioned before, the understanding between Sanzo and Kou, I think, goes beyond the general "reading your enemy" and Sanzo's natural ability to read people. Goku was saying it himself when they met Sharak, that the people at the top (namely the two high priests) must be lonely because few people understand the burden, even when they have people around them like Sanzo's bros. It's not the same. And the thing is, Kou is in a very similar position, with the very similar burden of leadership. It's not the same, and they aren't full mirrors, but that burden gives them a similar loneliness that Sanzo understands.
This exchange is really, I think, Sanzo's way of giving Kou what he himself got out of the Sanzo party - equals whom he didn't need to protect, and who would stand by him of their own volition, not because they feel obligated. It's indirect, naturally, because that's what Sanzo does, but it's something that he understands. And as I've said before, Kou was never truly their enemy (and Sanzo was the first to say it, so he's known all along). He's helped more directly in recent chapters, but this was the start.
Even later, Kou says to Ukoku as to what pulled him out - "I saw a light." As of now, only Sanzo and Kougaiji have ever had that specific imagery. Yes, Sanzo took Goku out of the cave and is described as "the sun" but it's very different - Goku was never in total darkness. He was /seeing/ a light he /couldn't reach/. Meanwhile, both Kou and Sanzo, for a time, were in /absolute/ darkness. Not unlike drowning. The "light" and "arms that always reach out for me" are very unique to them. And I'm sure Minekura did it on purpose, that these two leaders were pulled out of the "darkness" in the same way.
It's a subtle thing, first time you read it, but man is it obvious with a reread. And that's what I love about Minekura's stories.