"world size" is such a bull shit metric anyway. "oh this zone is 10km! but we made all our models 10 feet tall and they apparently walk at 100km per hour which is why it takes only 5 minutes to walk from one side to the other...."
literally take these "massive" worlds and have your character walk from one side of the map to the other. takes an hour? ok cool that means your entire fucking world is literally 3 miles (~5km) across, because that is the god damn average walking speed of ~6 foot humanoids. "ohh but we're running" ok then fine, in your fantasy world where no one ever gets tired lets pretend you pulled a forest gump and just ran from one side of the continent to the other...congrats, your world is 6 miles across.
Any other metric you use is absolute bullshit, no your game is not 500km or 2000km or whatever the fuck else you are trying to claim.
You can't make this ridiculous claim (1k+ km map!) then manipulate character models and movement speed to make the game playable or the zones manageable or to filter players together to congregate while also adjusting base movement speed to make it fit. It's bullshit.
Besides, the claim is a bold face lie right out the gate. Eve Online, for example, the largest zone is like 284 AU across or something. That's astronautical units (1 AU is the avg distance from the sun to the earth, and 1 AU is ~150million km)
How long would it take to "walk" from one side of that zone to the other? well in a very fast ship designed solely for speed doing say 10km/s you could do it in just north of 49 real life days. No shit you really can, you can set your heading and speed and just go AFK and watch as your ship slowly crosses the entire zone. Of course you'd have to log in each morning after server maintenance but you'd be where you logged off and could continue the journey, and just shy of 2 months later you would have "walked" across a single Eve zone. Keep in mind the speed of a normal ship is usually around 80-250 m/s, not km/s.
And that's to cross 1 zone. to cross the 8k zones of the Eve Universe? literally the sun will go red giant and wipe out life on earth before you could cross them all.
hell it took a player 224 days just to visit every zone, while using FTL warp drives/stargates Yet Eve never claims it's the "largest mmo world" despite the fact that it is demonstrably, unequivocally true. Because they aren't fucking retarded and any game that uses "world size" as a selling point is made by garbage people.