Awesome. Ok. I was hoping what I was trying to get at made sense. The second half of your sentence is spot on:
I would change the first part though to "complicates agency" instead of "limit it". This isn't exactly a 1:1 correlation, but its akin to the Wandering Monster clock in Moldvay Basic as it puts pressure on exploration turns in the micro and the entire dungeon crawl effort in the macro.
How do you feel about that change (limit to complicate)?
It's another tool in the box, and as such can be used well or poorly. Done well it's excellent and Heat is a great example (full disclosure: Blades is on my 'bucket list' of games). Sometimes it's lackluster, like with backgrounds and GIFT in 5e (which don't really work without a lot of effort). Sometimes it's bad. I haven't played any of the really atrocious systems, but they're out there.
And from there (assuming you agree), do you feel that setting/premise-integrated mechanical elements of play that thematically complicate decision-points and macro approaches to problems/aspirations increase verisimilitude?
I don't know, because I can't say for certain what's meant by verisimilitude. It's been overused and abused over the last decades. So, I can't say I really understand what you're asking by using that term.
What I will say is that done well, such rules really drive the theme of the game to the forefront. I'm not sure that's synonymous with verisimilitude (I'm super proud of myself that I've spelled that word twice now without speckcheck!).
That was what I was trying to get at with that post. My contention is that Blades in the Dark experience would be a much diminished experience without the feedback loop of Heat/Wanted Level and all its related components. It brings the setting alive. It makes the threat of the coppers or corruption amongst the luminaries/power players (especially given the Tier status, and therefore threat level, of those setting Factions) loom over your head at all times. It brings to bear the stress of desperation, urgency, and things spinning out of control (inherent to a doomsday clock) that should be present at all times for characters in a heist game where gangs of scoundrels are scratching and crawling (each others eyes out) to get out of the muck.
It would also be diminished if those mechanics were opaque/non-player-facing. Appropriate GM characterization and exposition can only do so much legwork. Well-integrated, thematically-appropriate mechanics bring the setting alive in a different way.
I'm not sure about the diminished bit -- to step away for RPGs for a moment, some video games have done an excellent job of hiding important systems -- you have to play until you figure them out and that significantly adds to the enjoyment. Now, sometimes those are accidental, and sometimes the designers expect you to consult external sources for assistance, but there still are a few good examples. I'd actually put Minecraft near the top of that list.
So, instead of diminished, maybe I'd go with much harder to do well. It would require the DM to be consistent in application of a hidden mechanic, and that's a tough ask. Tough enough that I guess I'd generally actually agree with your assessment, now that I've thought through the implications of my caveat: sure, it makes success at the intent harder to the point that the extent of success is diminished.
But, those kinds of things do require buy-in, and they are, sometimes, very apparently mechanical in nature. I suppose that cuts against some uses of verisimilitude (3!).
Tangentially -- I've long had a list of things that I'd like to modify about 5e (which, given my group, is the current game of choice). I enjoy 5e as written, but there are little things that either annoy me or that I'd like to see how they'd change play. However, maintaining a house rule bible is something I just don't really want to do, so I haven't. Until the game I just started a few months back. I decided I wanted to stress exploration more, and provide a game where the player's choices on where to go had weight. I wanted to avoid illusionism and not just move the planned encounters to the fork in the road chosen (not that I do that to begin with, but still, worth mentioning). However, in one of those 5e things I didn't like, many of the rules in the game actually act to trivialize the travails of travel (sorry). Spells, for sure, but some class features and even the resting rules. So, I took a look at the system and tried to make the smallest change for the biggest impact. Note, my motive for this wasn't that I think the resting rules are realistic or have anything to do with real injury and recovery -- I don't much care and have played many fun sessions with the default rules without a problem -- instead, I wanted to evoke that bit of trepidation in travel. I wanted the idea of straying from safety to be, well, not safe. So I slightly changed the resting rules and removed hp recovery from long rests. I also changed any saves to recover from or resist diseases or other long term effects to be at disadvantage. I then added a safe rest, which is 24 hours of downtime in a safe place, which restores hp fully and allows saves for recovering normally. This one change has completely altered how my group plays. They're still low level, and so they don't have many other resources to trivialize travel and exploration, but they now pay attention to time and plan trips so that they are not out overnight. It's also made wandering encounters much more impactful on the play (I used Xanthar's tables to populate a region with some monsters -- repeats meant a larger presence -- and then tailored my wandering monster rolls to match what's in an area. If the party clears a nest or camp, that entry is removed, resulting in safer travel the more they take time to eliminate sources of encounters). That one small change has made a huge difference in how my players play. So, I understand your point very well.