Dude, those suits existed technically, but peeps were not running on the battlefields of world war 1 wearing suits of armor with light machine guns. That's not what happened. BF1 is closer to a WW2 game then it is a WW1 game in terms of authenticity.
It's an issue of accuracy or realism, not so much authenticity. This is something that's been mentioned several times already but there's a difference between the two ideas.
They weren't running around like that, but it's portrayed in an authentic way - they aren't out of place with the context of a WW1 theme. That's what the battlefield series has always gone for, portraying the overall tone, atmosphere, uniforms, sounds, locations etc in a way that is authentic to the setting. It's the gameplay itself that then causes problems with accuracy.
In the same way here, the Katana, the Jacket, the Prosthetic are all authentic to the WW2 era - they all existed. The difference is in terms of the way they overall add together to create the overall feeling of the setting, it lacks cohesion because of the amount of out of place things.
You literally argued the oppoiste in your last post.
No, the suit existed, had relevance to the war, and the way it's put into the game tries to justify it being there even though it isn't shown in an accurate way because of that gameplay. That's different from the level of customization BFV is going for where it's "This existed so it doesn't matter if it really fits". It isn't just enough to be put in because it was around at the time, it also needs to be implemented in a somewhat reasonable way.
The aesthetics of it fit the time period and setting, but it was the gameplay didn't fit the real-life version. In this case the aesthetics still fit the era, but not the idea of a cohesive WW2 setting. It's to do with the scale of things and the extent of them coming together to overall affect the setting in a big way.