The problem with the players being given a series of immediate task by a superior authority is that it again limits the impact that player decisions to short term situations. They still go from point to point as they are being directed to by the GM as servants of NPCs who make the actual decisions where the story is meant to go.
It's certainly an improvement over an all railroad campaign, but still far off from the goal.
I don't think that having an initial goal makes the game a railroad. Nor do I think it must be far off from your stated goal.
I ran a campaign of Spire: The City Must Fall where I did this. The game expects that the characters are all members of the Ministry of Our Hidden Mistress, a clandestine drow group devoted to resisting high elf rule in the city of Spire. So the PCs are members of this group. I decided that to get the campaign going, I'd have their Magister (kind of their handler) give them a specific goal to achieve, followed by a broad task.
After the players had selected their classes and made their characters, we chose the district of Red Row to be the main focus of our game. It's a district riddled with crime, where three dominant criminal factions struggle for control. I decided that the Ministry's previous cell in Red Row was discovered and destroyed by high elf Paladins, the military group devoted to hunting down the Ministry. The cell's Magister was severely wounded and taken captive. When he wakes, he will be interrogated and may spill secrets. So the first task is to make sure he doesn't talk.
The second task was to then discover what led to the previous cell's destruction and what they were up to, and see if it could be used to hurt high elf rule in some way. So the players had an immediate task to deal with, and then an open ended situation to kind of explore however they wanted. This wasn't a railroad in any way. It was up to them to decide how to deal with the captured Magister and once that was dealt with, it was up to them how they engaged with the ongoing events in Red Row. Things quickly moved beyond the initial scenario and they became embroiled in all manner of things in the district, dealing with the three major crime factions as well as several other groups.
A big part of what made this work so well is that this is largely how Spire is designed to work. I don't think that can be understated. The classes all have elements that directly connect the characters to the world. They all have abilities that allow them to declare truths about the world. These factors make it so that the GM can't decide everything ahead of time. They allow the players to directly influence the events of play through their characters in a significant way, beyond just deciding what their characters do.
That default assumption permeates the game's design, so the mechanics and procedures of the game are not fighting against the players directing things.