Instanced housing is a technology that can be used to implement housing.

What many people asking for "instanced housing" really seem to be after is an unlimited numbers of houses: at least one house for every player, perhaps every character, and/or every FC that wants one. That's an actual potential game feature, for which instanced housing is just one potential delivery method.

So if that's what people actually want, they could prevent a lot of arguments (e.g. "FFXIV already has instanced housing") by rephrasing their request for what it really is: an unlimited number of houses. If they then want to argue that FFXIV can deliver unlimited numbers of houses using instancing, that's a sub-argument.