Oh, don't forget UT's genocide ending, where Chara says:
Oh I remember UT's genocide ending. In universe, Sans explains LV as your level of detachment from humanity, and EXP as your capacity to harm. Which doesn't really change in either interpretation of the world literally being a game or you player only interacting with it as a game, as either way its a part of the way the world works.
I think Chara mentioning GOLD is more revealing, as GOLD isn't some supernatural in universe magic force like LOVE. It's just literally gold, a source of wealth, Chara the demon in the genocide ending is talking about it self as a personification of that desire to see numbers go up and to wring 100% of the content out of something no matter what.
Which doesn't really matter if the world itself is a game, or if your interacting with the world like it's a game. As in the first case, those stats are just abstractions for the sake of you the player and you still like seeing those number go up.
The thing is the whole Alphys evacuating Monsters into areas you can't access do to your limited way to interact with the game, or Flowey's post pacifist ending plea only make sense if the world exist outside of the game. Flowey wants you to not do a True Reset as its the only thing that can bring the Monsters back into the game/narrative, but that desire is kind of predicated on a world existing outside of the game.
If there wasn't a world outside of the game/narrative, then there's literally nowhere for the characters to go afterwards and you not playing them game is them effectively being dead. Even as Asriel in his bossfight, his statement is more about how he'll outlast you until you quit. He says it himself, if you quit here and fuck off he can control the timeline as he wills. He wants you to put the game down so he can do what he wants. The world explicitly exists outside of the game and without the player here, elsewise his plan doesn't make any sense.
In the the genocide route, he's convinced that the Player is Chara, that you'll be able to leave the underground/narrative/game forever on your own terms with him. But Chara doesn't give a shit about that, and as a player you can only interact with the content in the game as is.
