I agree with everything you state here except perhaps a denial that 1 John 2:2 speaks of propitiation rather than atonement in general (it is not reading back into the Greek, "propitiation " has a specific meaning as does the Greek word...I take it you object to "propitiation", which is fair but I think propitiation serves your view just fine). But you are right that there are none "in Christ" but those who believe.
Sometimes it is hard to understand the posts of others. For example who denies that 1 John 2:2 speaks of propitiation? The verse says Christ is our propitiation. But what does that mean? It means Christ is our means of salvation. If a person is not "in" the propitiatory shelter of Christ, they are children of wrath. If people are transferred into Christ, they enter the propitiatory shelter of Christ, and are no longer children of wrath.
If we are not "in Christ" we are not in a propitious situation, facing the wrath of God. But if we are "in Christ" the situation is propitious, favorable, we are justified and united with God, our sins are forgiven.
I object to folks providing a special definition of a word, when the dictionary meaning works. Christ is the means of our salvation, He is the propitiation not only for us but also for the whole world. Everyone who is transferred into His shelter is saved, and everyone not in Christ is unsaved.