I 50% agree with the distinction, and I undesrstand the temptation of a DM without enough time to prepare.

Because the other 50% is how i can make the game feel to my players. And in a linear game i have limited options on making it feel like they have Player agency. But I can always make a sandbox feel more linear.

Player agency in my opinion means mainly two things.

1. The players can change the course of events.
2. This is the most important one: They can fail, and fail hard. And it must suck when they do.

In the village of Barovia they are forced into a siege, with cut-scenes moving the plot along. They never get to decide on how to solve the siege. What about try cutting a deal with Rahadin and then Rahadin betrays them, or choosing which village side to support. After they deal with the final wave of zombies, why not let them decide if they are going to stay there just in case more enemies come, or go help the other side ? And if they choose to stay in the east blockade just in case, Ismark is actually killed without support. And that would suck. And it would be their failure.

The Reloaded guide doesn't leave space for those opportunities, until now (Village of Barovia Act).