@NC-RetiredThat's a really interesting point, to me. I like that style (the MC talking to himself), but I think it's really a separate point, not an extension of the main one.
The way I see it, the first-person-narrator MC is a largely-reliable narrator of their story. They're not always 100% reliable for a variety of reasons: they may have misunderstood someone else, a situation, or whatever else. Perhaps they're '100% reliable' with respect to what they think happened, and when they're meaningfully not reliable, it should be noted as to what went wrong and how.
However, that has impacts on the storytelling. First, they're recounting a conversation that happened 'before'. How far before is nebulous, but their past-tense storytelling is both 'current' and 'time-lapsed'. Sometimes, perhaps, that condenses a A-B-C-D-A-C-B-A-C-D-A conversation into A-B-C-D or even A-B. 'Less important' parts are dropped.
Talking to oneself is even more elided. Instead of recounting a mental conversation, you get 'tell don't show' with the gist of the conversation turned into non-dialogue observations. If I have a series of thoughts on a subject, it's likely to be an 'essay-ified' version of something that was interior dialogue at one point.
And, yes, that loses something, but it also is easier for readers, so it's a tossup. There are good and bad points to either.
As one of those conversational digressions, there seems to be at least some evidence that 'talking to oneself' may be a sign of higher intelligence and is likely to be a sign of good cognitive function in general. Which is amusing, since I was part of a generation brought up with the notion that it was a sign of craziness and to be avoided.
My dialogues are always 'about something,' because the conversations 'about nothing and everything' get collapsed into some sort of 'tell don't show'. But my 'about something' conversations have become more digressive at times, because it does suit the characters and adds to the world.
That's also part of the author's dilemma. The more I 'show don't tell', the richer and more alive the world is, but if I was to 'show don't tell' the breadth and depth of conversations my characters should get into, I would run to multiple chapters per day, most likely. So there has to be some plot purpose for the conversations that are shown, and that focuses them more than the ones not shown, and maybe more than they usually are.
I'm pretty much out of chances for interior conversation with my MC except for the occasional bit, simply because he hasn't been doing it for 5+ books. But that doesn't mean another character couldn't do it in a side story, and I have side stories waiting to be told. Or do it in another story entirely :)