No, sorry, the 'immersion' argument is always lame.
Either for or against.
People get angry with a feature of the game, and that's fine. But when people start busting out "Plus, it's not realistic and it breaks my immersion" - that gets silly.
The bottom line is that when you dislike a feature, it breaks your immersion. When you like it, it either doesn't bother you, or you are willing to rationalize it so it doesn't break your immersion.
'Realism' is silly to talk about - the entire game is abstracted so far beyond reality and always has been - so the realism or immersion is entirely your responsibility. If it breaks your immersion, it's because you stopped immersing yourself.
edit: As for the actual topic, I don't really feel one way or the other. It seems like it would be an easy toggle to implement, but I think Spain is incredibly fun to play as because it makes geography matter, and you can get some ridiculously cool cities with those bonuses.
It is flat wrong... to even include El Dorado as a Natural Wonder in the civilopedia is wrong. It is a falsehood. It didn't used to be a natural wonder, it wasn't almost a natural wonder, it will not ever be a natural wonder. It is ignorant. It promotes ignorance. It is complete farce.
Movies of great battles are meant to mimic life. When you see a guy in a World War II movie wearing Reebok Pumps, you stop and say "What the eff is going on here?" You are less immersed. The same holds true for some people regarding these natural wonders in Civ V.
I can overlook Washington in BC because that is part of the game. Natural wonders a novelty piece of something from the world we live in. The planet Earth. They are called natural wonders because they occurred naturally on the Earth. You guys do understand that, right?
Prior to this version, the series did a good job to make a fun game and provide some information about the history of civilization. This game goes out of its way to promote ignorance. I know this is true because El Dorado does not exist. It's not an oversight or a bug. It is deliberately ignorant. The guy was a effing history major! They could have done anything. They could have made a separate label for non natural wonders. They could have added real natural wonders. Instead they went for ignorance.
Needless to mention, that was their idea of improving gameplay and making for a more enjoyable game. Add some natural wonders. Wow! The least they could have done is add some natural wonders and not some thing from the days when Spanish Ignorance plagued the New World.
Hiawatha, might be fictional. I don't think anyone knows. He was still a revered leader of the Iroquois. There is a major difference there for me and I can't say why. I don't know how to express it.
Immersion in movies, in art, in video games exists. It's different for different people. The argument has been expressed in many ways and some people see it, some don't. They used actual things from Earth because the game modeled civilization. This isn't Stronghold Legends. Stronghold Legends promoted the use of fantasy units at least. Civ Legends. Spawn Merlin from a CS, while you are adding new gamebreaking content. Maybe he can count as a settler which settles "Magic City" and that city is invulnerable to attack. It adds an element of mystery and intrigue to Civ. You know, because that's all that was missing in Civ V. A little excitement and mystery. LOL at CIV:Legends.
Like I said, they can save face and have Fake Natural Wonders "On" by default, but the button really should be there. Call them whatever they want... Fake NW, Make-believe NW, but the button should be on there... they could also do "True Wonders Only On/Off" etc.