of course the horizon is lighter, get close to any building on the horizon and look at the textures, the horizon is made for you to see things from afar, the odyssey is made for you to get close, there is no magic, you need to put textures there and that weighs.
If you compare uncapped frames you’ll see that EDO has about half the frames that Horizons gets even in deep space when not surrounded by anything. Someone gave an example of that earlier in this thread.