I completely agree with you that this cannot possibly replace other measures such as masks, hygiene, and avoiding large indoor gatherings. Nor should it.
I think there is an additional confusion though. This is really an exposure notification app. If you used only this, and not traditional contact tracing, you would have to have a lot of adoption. But I think the general recommendation is to use both (1) these exposure notification applications and (2) traditional contact tracing by people trained to do it. Then you don't need as large an adoption to get utility. Traditional contact tracing can be effective, especially for people you know you contacted. But it is slow, and does not handle well the people you don't know. By combining them, there is a greater odd of notifying those who may be potentially infected. As long as you're also doing traditional contact tracing and other measures, a lower adoption rate for these applications can still be valuable.
Full disclosure, I work for the Linux Foundation. But I still believe this anyway :-).
I think there is an additional confusion though. This is really an exposure notification app. If you used only this, and not traditional contact tracing, you would have to have a lot of adoption. But I think the general recommendation is to use both (1) these exposure notification applications and (2) traditional contact tracing by people trained to do it. Then you don't need as large an adoption to get utility. Traditional contact tracing can be effective, especially for people you know you contacted. But it is slow, and does not handle well the people you don't know. By combining them, there is a greater odd of notifying those who may be potentially infected. As long as you're also doing traditional contact tracing and other measures, a lower adoption rate for these applications can still be valuable.
Full disclosure, I work for the Linux Foundation. But I still believe this anyway :-).