Finally, PCs have very little control over not spending stress. Losing 1 stress is called out in the rulebook as a consequence of succeeding with Fear, and several enemies do Stress damage.
Sorry but it's just not accurate to claim PCs have "very little control" over Stress. They don't have total control but it's basically a resource they are generally in charge of in a way that's not true of HP. And my point isn't that the players will succeed, it's that they'll naturally try if you keep forcing attrition-based days on them, because it's the logical metagame response. It won't actually stop them getting attrited, to be clear - it'll just mean that they play more boringly and conservatively as a result!
Also, maybe beside the point but any DM who
routinely (i.e. multiple times per session) charged Stress for succeeding with Fear would be
massively nerfing the PCs (crippling them, it'd be fair to say), and frankly it's unreasonable behaviour and a outright bad suggestion (pretty much all RPGs have some of this, I note, especially in first editions). I can't find where in the rules they outright suggest that, but they should not, frankly. It's not okay, because it's actively breaking the principle that success is success, and you can't take away that success by the "with Fear" complications - if they're so severe that they do, they're too severe - and in most cases charging a Stress for your already-achieved success is absolutely that (the exceptions would generally be very extreme circumstances). Certainly the threshold for charging Stress should be very similar to the threshold for charging HP (a little lower because you get 1 Stress back on a critical success, but not much). Are you thinking of the "Stress from complications" section? Because it doesn't say "Oh you can casually demand Stress for simply rolling with Fear" that, and would be in danger of breaking its own principles if it did. Plus this examples it gives are not routine, every-session examples, they're extreme ones, like "committing an act of incredible bravery" (to me that means something like voluntarily leaping through a sheet of flame or the like). I doubt there's a single example of any DM actually just randomly charging Stress on a success with Fear in any actual-play of DH, too, because it's so obviously unreasonable in play. It's only going to be in some fairly insane circumstances, and likely to avoid a worse complication.
There are enemies who do Stress damage, but they're not some constant, and most of them will only actually get to do Stress damage at most once or twice in a combat before they're taken out (in many cases they won't get to at all).
Let’s say, 4 Minors and 2 Standards. You spend 1-3 on the Minors and 2-4 on the Standards (though to be fair, I agree with you that the estimates for these encounters in the book seem low). With those assumptions, at the end of the day, you spend 14.
On the other side of the ledger, you have no. of players + 3d4 + Fear generated by rolls. I think you could get less than 26 (14 + 12) with that calculation.
As soon as you run the game you'll see this isn't plausible.
14 Fear, even assuming zero monsters generating Fear means about, what, 32 rolls? You genuinely think it's plausible that the PCs will resolve six (6) encounters in 32 rolls? I.e. about 1.3 rolls per PC per encounter? Because having played it, I think it's barely plausible that they'd resolve two (2) combat encounters in that few rolls! And remember, "minor" encounters aren't real, defined thing - they're
back-defined by how little Fear you spend on them. But realistically as we're seeing that's going to mean just sitting on 12 Fear a lot of the time if you want to only spend 1-3 Fear on entire-ass combat encounter. On average, 3 Fear is 7 rolls. It is very unlikely the PCs can delete an entire encounter in under 7 rolls. So you can try not spending Fear but the numbers they quote are unrealistically low (again, first-edition syndrome).
The closest thing to a defined "minor encounter" too is spending (number of PCs x4) -1 points rather than number of PCs x4 too (which I can assure you is not a huge difference). I mean, realistically, experienced DMs are going to sometimes throw undersized or even single-monster encounters at the PCs (I did), but the actual rules don't really account for it (an oversight imho).
I'd say the guidelines on Fear spend are just generally not realistic compared to how much Fear is actually generated in the game or indeed how much Fear it costs to make an encounter feel alive (especially if you're not using a lot of Leaders as force-multipliers).
On top of all this, DH encourages the DM to allow the PCs to resolve encounters without resorting to violence. This means you could end up generating a lot less Fear, because it'll probably be far fewer rolls (or maybe none at all), but it goes directly against attritional play, for the same reasons - it's unlikely to use much in the way of resources.
I think this discussion is helpful in that it highlights three areas of improvement for DH for later editions:
1) Fear spend guidance is not good (in both directions).
2) Guidance on what costs Stress is inconsistent with itself and possibly the principles of the game, and Stress as a mechanic is a little inconsistently treated (is it a resource or not?).
3) Lack of real rules for more/less threatening encounters is unhelpful (literally the entire guidance is you could subtract one (1) point to make an encounter easier or add two (2) to make it harder - that's it!).
4) Monster costing based on roles is inconsistent with how they perform in-game (Leaders, for example, can be huge force-multipliers, and charging less for them than Bruisers doesn't really fit - also some monsters in the same role, in the same tier, have far lower stats than you'd expect and this never seems to be accounted for or clearly explained).
