It's becoming an interesting question. When I think of salads in the So of France, they are
basically with really good (and that makes a difference as well) olive oil with just a hint of acid, usually lemon juice. Tending not to use much else and relying on the freshness and flavour intensity of the salad ingredients. Simple.
Winter salads, maybe in the north, are more reliant on the zing of the dressing to compensate for understated flavours of the major ingredients. So often shallots.
In Italy, my recollection for the most part, is just oil, and add something else squeezed over if needed.
But I am not crazy about salads here, in general, and I rely on shallots in my vinaigrette: REALLY wonderful olive oil (Basilippo from Spain), hazelnut oil, and a spot of Dijon. But still, I think about 3:1, again depending on what I have done with the shallots in advance. Depends on the oil, what it is dressing, whatever herbs may be added.....
I think our tomatoes don't compare with something picked off a hillside in Italy, with enough acid and excitement not to demand much of a dressing. The heat of the sunshine still resides in those tomatoes and killing it with lemon juice....is just not likely to happen. The romaine that I get at stores here, needs to be attacked by a dressing to get the plastic flavour and smell out of it. In Europe, in would be more difficult to find romaine that even smells unappealing in the store.
In most cases, in Europe, you mix your own at the table as you eat it.
And it may be possible that our tastes are changing from the days of Pepin and Child.
It depends.