If you shine a flashlight through a tree blowing in the wind and vary the brightness to convey information, the signal can get distorted pretty easily.
However, if you have a constant brightness source and vary the color, it’s a lot easier to figure out what the source is trying to convey.
It's like saying that the violins is merely an analogy for how a double base works.
Rubber ducks aren't battleships because they both float. Visible light and radio attenutate in meaningfully-different ways. It's an analogy.
Yes. Just like light and radio waves are both EM. A rubber duck remains an analogy for the buoyancy of a battleship. Not "literally the same" thing.
For me, the people saying they are the literal same thing are the same type of people that gave me that "aha" moment that really helped solidify my understanding of RF.
It was pretty mind blowing when I Understood that AM is a change in brightness and FM was a change in color. We just can't see RF, but if we could, that's what it would be.
But battleship doesn't equal floating in water, floating in water is a property it has.
If you're saying "the way a battleship floats in water is like how a rubber duck floats in water" then it's not an analogy, it's as you say just describing two versions of the same thing.
But it is an analogy to directly compare the two objects, because "floating on water" is a property of the objects it's not the object you are comparing.
Wikipedia begins its page on analogies with this, sourced from The Oxford Companion to the English Language: "Analogy is a comparison or correspondence between two things (or two groups of things) because of a third element that they are considered to share."
Or Marriam-Webster: "a comparison of two otherwise unlike things based on resemblance of a particular aspect"
Apart from rubber ducks and battleships both having the "third element", or aspect, of "primarily used for floating on water", they are definitely two completely different things. Nobody could look at a rubber duck next to a warship and say "they seem to be the same thing".
The more closely related two things are the more useful and less stretched the analogy available, which is why the analogy about radio waves was so enlightening to so many people in this thread. But it's bang on as the definition of what an analogy is.