Not true. I personally hate that most of new games are designed as hub walks. Go to hub, do tasks here, move to next hub. That’s not different that invisible walls, and closed corridor design.
Big open world games are fun, when you don’t know what to expect and when to expect something. Big open world games need to be designed around emergent gameplay, not directed one. You must embrace he fact that play can and will do things in your game that you did not predicted.
As for question why walking is gameplay in MMO. If MMO is open world, with PvP, you can always walk into another player.
As matter of fact walking is big part of gameplay even in games like Skyrim, or recently DAI. And I’m honestly bit disappointed that DAI do not have bigger zones, which just look cool and doesn’t have anything particular to do except walking around.
To each their own, but I think directed and clearly defined gameplay experience in big open world game, is just bad design, which just works against what players expect in those games.
People who like directed experience will not like the fact that there is open world, and people who expected “i can do whatever” will be disappointed that game have clear boundaries.