IMO, it’s nigh equally likely that they started with the verticality design as part of it and didn’t have the time to cook the idea into something neat, vs it being a later mandate after some core designs had development.

Well it's a good thing that we have commentary directly related to this then, alongside basically ever major development decision... Because that's apparently what happened...

https://kotaku.com/how-biowares-anthem-went-wrong-1833731964

As development progressed, it became clear that some of the Anthem team’s original ideas either wouldn’t work or weren’t quite solidified enough to be implemented. Take traversal, for example. The mandate was that Anthem’s world would be massive and seamless, but how would you get around? The team played around with prototypes, exploring different ways in which your exosuit could move vertically across the world. For a long time they thought it’d be climbing up the sides of mountains and ledges, but they couldn’t get that quite right. Early iterations of flying—which, developers say, was removed from and re-added to Anthem several times—were more like gliding, and members of the Anthem team say it was tough to get the system feeling all that fun. Every time they changed the traversal, it meant changing the world design accordingly, flattening and stretching terrain to accommodate the latest movement style.

The most common anecdote relayed to me by current and former BioWare employees was this: A group of developers are in a meeting. They’re debating some creative decision, like the mechanics of flying or the lore behind the Scar alien race. Some people disagree on the fundamentals. And then, rather than someone stepping up and making a decision about how to proceed, the meeting would end with no real verdict, leaving everything in flux. “That would just happen over and over,” said one Anthem developer. “Stuff would take a year or two to figure out because no one really wanted to make a call on it.”

Certainly sounds like the developers had no idea how to make the game.

One longstanding BioWare tradition is for their teams to build demos that the staff could all take home during Christmas break, and it was Anthem’s turn during Christmas of 2016. By this point, BioWare’s leadership had decided to remove flying from the game —they just couldn’t figure out how to make it feel good—so the Christmas build took place on flat terrain.

Around the same time, Electronic Arts executive Patrick Söderlund, to whom BioWare’s leadership reported, played the Anthem Christmas demo. According to three people familiar with what happened, he told BioWare that it was unacceptable.

Now it was time for a new build. “What began was six weeks of pretty significant crunch to do a demo specifically for Patrick Söderlund,” said one member of the team. They overhauled the art, knowing that the best way to impress Söderlund would be to make a demo that looked as pretty as possible. And, after some heated arguments, the Anthem team decided to put flying back in.

So they removed flight entirely by Christmas of 2016, that would mean the entire map design had to lose the verticality. If you can't fly, then you have to flatten the world do accommodate for ground movement instead.

And it was an EA executive that got them to put flying back in as a focus, flying that the team had removed entirely by that point. Even if they weren't specifically told to do so by EA. And then designed the entire game's map and movement based around that flight by the launch just over 2 years later in Feb 2019.

They were clearly meant to fly in some way, even if it might’ve been in a Halo jetpack sort of way early on. (which has less evidence)

I love that you try to hedge your comment and try to say that jetpack jumps and gliding are somehow even remotely in the same ballpark as flying around like Iron Man. You're honestly trying to say that Link or Aloy on a glider is similar to Anthem's flight? That's a ridiculous thing to try to compare as similar.