Celebrim
Legend
I think we have different ideas of how a downtime activity is run. In my mind, the downtime activity rules are there so you can handwave away whole categories of endeavors that don't require in-character interaction between the PCs and the DM and are mostly outside the story. It seems to me that resolving downtime activities should take about the same amount of time at the table as figuring out how much gold and how many days it took the wizard to make a potion. My personal opinion is that options like carousing (and maybe running a business) are there so that every player at the table can say they are doing something as you go around to check on how they intend to use their downtime.
I completely agree. Speed of resolution is always - regardless of what the rule is intended to do - a major factor in evaluating whether it is a good rule.
But it's not the only factor.
Some other factors:
a) Does the rule have a purpose? If the rule offers insufficient reward for the cost of performing the task, no PC will ever do it (except perhaps the few times necessary to see that it doesn't offer a reward). If you print a rule that is specifically designed to discourage someone from doing something, that's probably a bad rule. If you print a rule for something that isn't important to the game, its a bad rule. Conversely, printing a rule suggests that it is important to the game.
b) Is the rule balanced? This is the opposite of the first point. If the rule offers too much reward for the risk, then a player with the aesthetic motive of play of 'winning' will be motivated to only make that 'play' - and so will both break the game and be bored and feel its the games fault. And frankly, he will be right. So often I see apologists for rules saying, "So what if the game is unbalanced. Just don't play that way.", and these people just don't get it.
c) Is the rule sufficiently associated with the thing it abstracts? Every rule is an abstraction of a more complex reality, but if rule doesn't associate with the imagined reality it loses its power to create believable narrative. It's something of a matter of taste how strong the association needs to be, but it needs to be there at least a little. In the case of rules for combat simulation, at the minimum it needs to make the character that is more skilled at combat more likely to win the combat (rather than counter-intuitively less likely). In the case of an economic simulation, I'd expect the same sort of concept to be present - the more skillful you are supposed to be at the task having economic value, the more likely you are to turn a profit. So for example, if I own a tavern and my character has proficiency in Craft (Brewing), Craft (Cooking), Perform, Knowledge (Math and Ledgers) or whatever the system provides for, then I would expect to turn profits more consistently than a character that was inept at these things. The more level of detail, the more different inputs might be accounted for, but even minimal inputs only require about a sentence of reference and calling out a bit of minimal DM judgment.
One additional point can be made by highlighting a sentence in your above quote: "In my mind, the downtime activity rules are there so you can handwave away whole categories of endeavors that don't require in-character interaction between the PCs and the DM and are mostly outside the story."
You are exactly right. And because you are exactly right, the same rule should work as well for PCs and it does for NPCs - not because the rule intends to create a simulation of the world or needs to or any other straw man argument people keep throwing up - but because if NPC activities pretty much exactly fall into the category of things that can be handwaved, don't involve interaction between the PC and the DM, and are mostly outside the story. If the rule doesn't work for NPCs in this situation, you can be pretty much assured it doesn't work for PCs either. And any rule that would work for NPCs in this situation, would work for PCs with only the minimum amount of adjustment depending on how much rules were shared between them. In 5e case, with regard to economic activities, the answer is sufficiently close to 'all of them' that the rules could be insensible to the difference.
I don't necessarily see the accuracy of the economic rules for running a business (especially as a downtime activity that doesn't really happen in-game) as very important.
You keep saying that sort of thing as a defense of the rule. I'm baffled, because from my perspective you keep damning the rule.
In the DMG, one doesn't necessarily expect to find something as complicated as the stronghold rules in Pathfinder's campaign guide. But to the extent one expects them to show up at all, it's reasonable to expect that they should have the same design intentions as the rules in the Pathfinder campaign guide.