We had earlier agreed that the bride of christ is indeed historical, but it is a metaphorical term referring to the people of God. We are not “in the bride” as much as we are “in Christ”… as the church (people of God) we are actually the bride, married to Christ. But it is symbolic language… we are also brothers and sisters of Christ, and we are also his friends, and we are his children.
Since Paul was not discussing Adam as merely figurative, but only our relationship with Adam is partly figurative and partly obviously real; we are actually descendants of Adam as he is the progenitor of the entire human race. We are connected in a real sense.
Most importantly, as you said, Paul does talk of sin entering through one man. The consequence of that was death. Paul was indicating that real death entered because of sin. “Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned—…” No one escaped this sin, and no one escapes the death, both of which came through Adam. You cannot separate this. “in this way death came to all people”. In what way? In the way of sin entering thru Adam. Death came after sin, all sinned, and all will die. Unless you can demonstrate that someone else besides Christ did not sin, you know that sin entered and spread to all. Entered through the one man, Adam, and spread to every human being, all people.
“For as in Adam all die, so in Christ all will be made alive.” Just as Christ was a real person, so we know that Adam was a real person. As we are all affected by Adam, so we can all be affected by Christ, in his redeeming sacrifice of love on the cross, and his victory over sin and death in the resurrection.