That may be true, but we are discussing an American idiom.
When a young man asked where the public telephones were, Dorothy Parker was supposed to have quipped “He really needs the bathroom, but he is too embarrased to say so.”
I’ve heard the Brits don’t use the term - Loo much anymore. Isn’t it considered vulgar like The John?
I watched Changing Rooms (a show on BBC America) a lot and they never referred to the restroom as The Loo.
“Loo” has always been slangy, at best.
Oh, yeah. It’s far better to not know the difference between the room and the porcelain throne.
And it’s not like toilet isn’t also euphemism. You guy took it from the French. From the original article by Cecil, it would seem that it originally meant something close to dressing room. Your version makes eau de toilette sound really nasty.