We are talking about smart home things here though, which usually depend on their own services anyway. This is more of a problem with things like Windows reach

We are talking about smart home things here though, which usually depend on their own services anyway. This is more of a problem with things like Windows reaching out to msftconnecttest.com or some other generic internet service. But in the case of a smart home device it's needs are usually more well defined. This becomes harder with a consumer router trying to determine if it is online though unfortunately because of exactly what you describe.