The missions in Asylum were designed so you never had to traverse the map too much to get to start the next part of the story. Yes, it was like a mini open-world though it still shared a lot of linear single-player traits with its mission structure. City ditched this, having the player traverse the map back and forth, sometimes from one end to the next. It's not that I thought the open-world ruined AC, it was just incredibly unneeded for that type of game.
And in City you always have the next objective on your map and the points of interest are the individual locations—the "linear single-player" traits are still present (and improved over Asylum) in the Wonder Tower, steel mill, underground League of Assassins hideout and Strange headquarters areas. Then there's sequences that leverage having an open environment like the sniper gauntlet before reaching the final Joker encounter. The only difference is that player isn't constantly funneled down linear paths that they have to immediately backtrack down to get back to the still protracted, empty hub. If Asylum actually had a well-designed Metroid-style overworld that had clever spatial puzzles worked into the level design and looped back upon itself in interesting ways, I would understand how some bristle at City's approach, but Asylum wasn't special in that regard.
If there's nothing to do in City's overworld, then Asylum's is way worse. Even just the Riddler content from each game encapsulates how City is better than Asylum. Both have Riddler trophies to collect, yet backtracking through Asylum is a dull nightmare where you're on foot going through loading screens nonstop, picking up trophies that are either just sitting around a corner or are behind a weak wall and that's it, not to mention all you get is an audio file as a reward. City makes that sidequest actually worthwhile, makes traversing the overworld meaningful through tracking Riddler henchmen, the puzzles and hostage deathtraps involve actual puzzle-solving that makes use of the game's mechanics and player abilities, and it culminates with Batman actually getting to confront and catch Riddler himself.
Rockstead knew what they were doing with that game and comprehensively improved on what they did before.