styx in the river

if the goal was for Dutch to throw out an example of someone who was loyal and contrasted from Arthur's current questioning and what Dutch perceives to be "doubting", he would've had a far better chance of actually being convincing in throwing out that example of contrast had he mentioned someone like Javier rather than Micah.

Arthur sees Micah as a loose canon, not someone he can have faith in to not lose his head or lead the gang into danger. He already even expressed as much to Dutch more than once by now, even in this chapter itself

So it's not as if Dutch doesn't know this.

But on the other hand, someone Arthur does still have respect for at this point who is loyal, is Javier. Javier expresses his loyalty to Dutch in the fishing companion activity, in which he states that no matter what they have to do or where they have to go or how much blood needs to be spilled, Javier will still stand behind Dutch

But I will say that he can be caught questioning Dutch before Guarma at least once

And then Arthur then can proceed to tell Dutch this and get back this response

So all in all, this tells me two things about where Dutch's head is at:

Micah is already living rent free in Dutch's head by chapter 4. As I've shown, Dutch brings up Micah out of nowhere more than once in this chapter and Micah barely even has a presence in the chapter itself, save for camp interactions, a companion activity, and his inclusion in the bank robbery at the end of chapter 4. He's at the forefront of Dutch's mind when he needs an example of loyalty, because...

Dutch is showing his hand here that he wants blind loyalty. He doesn't want to be questioned at all. Questioning his choices even a little bit or bringing up different options other than the one he wants to pursue is, to Dutch, a sign of disloyalty. He doesn't want the gang to think for themselves or criticize him because they might realize "hey maybe following this dude into the darkness is a bad idea". He needs a yes man, an enabler to make even his most terrible of choices feel good, and he won't listen to reason. He detests logic and reality for the mask of fighting for a dream, for an idea, when he's really little more than what Milton says he is: a killer. And he only shows his true colors more and more throughout the course of the game until he's no longer hiding it - still hiding behind the dream or idea, but being far quicker to jump at the opportunity to cause chaos without restraint. That's why Javier's loyalty doesn't even occur to Dutch to suggest to Arthur in place of Micah, because though Javier is extremely loyal, every now and then he would still question him until chapter 6 where his loyalty is finally more welcomed as he completely stops questioning Dutch.