Ovinomancer
No flips for you!
So, yeah, there's a pretty big difference here that you've papered over. In Blades, the fiction is "what has been established in play." Further, the GM is constrained by what the player wants. The "subjective" GM decisions present in the play example are really whether or not to call for a check and then how to enact consequences on the failures.It is interacting how with that Blades examples all the subjective calls the GM must make are described to 'be dictated by the fiction' etc by the same people who think that in GM driven game players have no agency if the GM decides things, though of course in such game too the GMs decisions are equally dictated by the fiction present.
For whether of not to call a check, this is "subjective" (scare quotes intentional) but not arbitrary. It's subjective only in the fact that it's a judgement call, but one strongly guided by the game's rules and principles. @Manbearcat posted the relevant rules sections above. Here, the player was declaring an action that was important to the character -- it was an opportunity to make steps along the hard change in vices. The rules tell you this is a good point for a check because just saying "yes" robs the import from the action and turns into the GM waffling to make life easy on the characters. This is NOT what you are supposed to do in Blades -- you are supposed to be a firehose of adversity turned onto the characters. Why? Because you're a fan of the characters and want to see them shine! To look at a different example, we don't watch Die Hard to see John McClain relax comfortably at home, we watch because we're fans of seeing how he overcomes the avalanche of adversity turned upon him. This is the play that Blades is designed to develop -- there are very few calm moments in Blades.
The second "subjective" thing is the consequences leveled. And, here, yes, the GM is absolutely using their authority. There are walls to this though -- the "follow the fiction" restriction means that the consequences have to make sense within the fiction as already established in play. This is different from 5e in that there are no GM's notes, or established fiction that has yet to be presented in play. IE, there's no GM note that this painting is a soul-sucking painting anywhere. Instead, the Blades GM has to either play up an established part of the fiction or something that flows directly from the establish fiction, or make a "soft" move to introduce a new threat but can't pay it off, yet. The GM is further constrained in consequence by the nature of the action -- the consequence should flow obviously from the action taken. You Attune the ghost field? Ghostly problems. You Wreck something? It's very noisy, guards come to investigate or you accidentally damage or break it. Etc, etc. Actually, Wreck is a good example, because it allows my to point out that characters have special ways to affect these actions with their playbooks (think class). The Leech in my game chose a playbook option that allows xer (the character is non-binary, the player is a her) to Wreck quietly, so I can't level "it's very noisy" as a consequence when xe Wrecks things. Finally, the GM is constrained by the agreed to risk, or position, of the action. I can't level a Harm 3 on a Controlled action, and I can't level a Harm 1 on a Desperate action, for example. These positions require that the consequences be in line with the danger of the action.
So, yeah, there are judgement calls in Blades. However, these are pretty tightly constrained by the rules of the game. Compared to 5e, say, the GM in Blades has many, many fewer places they can exercise authority, and in every one of those cases that authority is constrained in ways that they are not in 5e. Some of these constraints are generated by the system, others are generated by the players. The effect of this is that the GM in Blades has much less agency than the GM in D&D. The players in Blades have more agency because they can do pretty much all of the things players in 5e can do, but now many of those same choices are binding on the GM. The constraints on players exercising control over their characters is the same as to D&D -- any cases where you might feel this agency is impinged (ad argumentum) I can point to similar cases in 5e, many of which are even more severe. And, again, in my Blades game, these impingements are things like being confronted with an angry manifestation and having to make a Resist check to not lock up or flee in fear. That's something that's extremely common in D&D. And, that's really the only point that's come up in my Blades game. I suppose that if you're up against some of the more occult horrors, other things might also happen -- a vampire might charm you on a fail, frex -- but this also isn't any different from D&D.
I know that the response to this will be to wave vigorously at the caricature of Monsterhearts, and to be fair, I haven't read the rules but I have read it's concept and I am familiar with the rules it's based on. I understand how it plays, and yes, the players do choose to have less agency to determine their character's emotional state when they choose to play the game, but this isn't comparable in general to 5e. The point of the game is to explore your character's untrustworthy feelings as they navigate adolescence as a monster. This is a fundamentally different focus of play, and the players are given additional tools to enact this that are missing in 5e. When we say, "you have less agency in this specific area I'm going to argue about," we're running straight into my argument that there are no "types" of player agency and that saying so obfuscates things. Here, you're trying to claim a victory by narrowing the discussion to a specific point you think you have a good case for (it's iffy, but let's say okay). However, when you do this, you're completely ignoring the other areas where agency is increase with these additional tools or the constraints placed on the GM, or... etc, etc. When looking at agency in a game, this is a bad evaluation. If you're saying what you like, then it's relevant -- but that's an argument about what you like, not an analysis of the game.
I'm sorry, but the player decided the painting was potentially important to something that was very important to the character -- this isn't flavor. Further, the kind of consequence was also chosen by the character, and they chose to engage in an area they have little to no ability because it fit their character's agenda, personality, and drives. They really wanted to repair their relationship with the University and overcome their disgraceful exit from the University that was caused by his gambling problems (all player defined). So, the player wanted this opportunity to help his character's cause, and knew that a quick route would be to deliver occult items, even though that wasn't his character's forte. And, he could have waited for the Whisper to do it better (the Whisper is good at the occult), but felt his character wanted to keep this on the down low because he hadn't opened up to the Crew about his disgrace or gambling habits. This was entirely in-character motivation, very deep, and involved complex motivations. I didn't expound on this before because the example was to show how foreshadowing works, not an examination of why the players have chosen what they chose. But, this wasn't flavor or flavour, it was assigning importance to things because the character cared about them.Also in the Blades example the player getting to choose the flavour of doodah they poke and the flavour of bad stuff being tangentially affected by that is seen as player being able to direct the fiction yet the same people see characters talking, having emotional reactions etc as inconsequential flavour.