They really aren't constraints. If that's what it sounds like to you, look at the rules for Blades in the Dark. If anything it's the lack of constraints that tends to freak people out.
Story now games are much, much more surprising, since you aren't just watching PCs move within a relatively narrow range of freedom. The entire narrative flow can change direction at any point. Maybe a success-with-consequence that a player rolls has you saying that a blizzard is rolling in, or that a cop shows up. Or a miss on a roll might mean an ally turns out to be a traitor. You could say that's all just improvisation, but it's far more improv, to a much greater degree, and with very different triggers.
Again, I think you're forming some pretty hard opinions--and spending a decent amount of time expressing them--without really looking at the material. Older PbtA games might have really pushed the idea of a set list of GM moves, but that's basically gone in newer games. Thirsty Sword Lesbians has a list of sample GM moves, but they're just suggestions. Brindlewood Bay and The Between suggest possible consequences, not moves. The point of most of those suggestions is to help the GM with all of the improvisation they have to do.
One of my favorite consequence suggestions in Brindlewood and The Between--and one that I think illustrates how different this approach is from a traditional game's--is to split up the PCs. That's something that, in other systems, might require a flurry of rolls and back-and-forth, and could be met with the usual panic over player agency. Perception rolls, Dex saves, Willpower checks, etc. to stop the door from locking behind you, or to resist the hallucination or spell drawing you away from the others. But in horror/investigation narratives getting split up is a pretty common trope. So if a consequence is rolled, and it works in the fiction, it can just happen. And that's not based on the GM triggering the "Split up the party move." It's just one of many possible consequences.
And in Scum and Villainy, the list of suggestions is framed like this:
"GM ACTIONS
In the same way that player characters have actions they can use to get things done in the game, so do you have a set of GM actions. When you need to contribute to the story and you are unsure of what to do, look at this list of actions and pick one."
Just suggestions. Ultimately, though, it's obvious that you're opposed to this approach, and you don't want to try running one of these games. That's totally your call. Just seems like you're spending a lot of time and effort pushing back on something you don't really get, and don't really want to.
And on the topic of 'GM actions', its not like they are in any way constraining. In Dungeon World the game literally says "GM moves are just what you have always been doing as a GM." And they are COMPLETELY open-ended. Like:
Use a monster, danger, or location move (these things can be assigned moves in prep if you wish, though honestly I never bother)
Reveal an unwelcome truth
Show signs of an approaching threat
Deal damage
Use up their resources
Turn their move back on them
Separate them
Give an opportunity that fits a class' abilities
Show a downside to their class, race, or equipment
Offer an opportunity, with or without a cost
Put someone on the spot
Tell them the requirements or consequences and ask
There is also a list of 'dungeon moves'
Change the environment
Point to a looming threat
Introduce a new faction or type of creature
Use a threat from an existing faction or type of creature
Make them backtrack
Present riches at a price
Present a challenge to one of the characters
I mean, if you look at these, they're all actually pretty general and overlap a lot, they are more ideas for things GMs can do to 'make fun happen'. I mean, 'Reveal an unwelcome truth' is so general it is just "give out some bad news." The DW GM is not naming moves, there are NO RULES for any of these moves, except maybe the rule that a 'hard move' deals damage or is otherwise directly harmful to at least one PC, while anything that just ups the pressure or creates an indirect threat is a soft move. Technically the GM pretty much use either whenever a move is invoked, and that happens when a player rolls 6-, when the players ask you what happens next, and whenever the players hand you a golden opportunity (basically ask for it).
DW is really an amazingly simple game (well PbtA in its general form is). It is completely open-ended, just like any trad RPG, anything can happen (I mean, perhaps bounded by the D&D-esque genre, but that doesn't put many limits on things, frankly).
