Well exactly so.
If the Pastor's sermons are according to Scripture, they carry authority, or should do.
A creed or confession is the same.
It carries no authority in and of itself, but if it agrees with Scripture, and to the extent that it does, it has the authority of Scripture
Every church IMO should adopt a clear, Biblical confession of faith for the reasons that I have outlined, which lays down what that church believes.
It thereby holds new members and new Pastors to that belief.
I repeat that I would never join a church that did not have such a confession.
It will almost certainly become liberal at some stage.
I think you are missing the point (because you keep going back to a role of confessions upon which we agree).
I agree statements of faith are wonderful. They let those within and without know what a congregation believes. But I do not believe they are an authority. They are expressions of common belief - NOT the authority for that belief.