Your argument doesn't follow if Paul's use of quotation and antecedent are even slightly other than what you say they are. You feel very strongly that Paul's language choice indicates General Atonement, to the point that you feel Paul would be misleading his audience if he wrote something that brings up these feelings within you but didn't mean to. But if you can't explain why this is the case from a technical, linguistic standpoint, I can easily write off these feelings as eisegesis. You are Arminian, therfore this is what you expect to find in a text, so when you read a text, you find what you expect, not what's there.
I will try to write the technical argument I'm making in the most introductory of terms. Human language has the capacity to refer to things not by their actual, individual name, but by features they have. We call these pronouns. In Indo-European languages, the features defining pronouns are person, number, and gender. In other language families, a pronoun can indicate the social status of the speaker. But there is a limit to what a pronoun can indicate.
For instance, the human brain probably would be unable to handle a pronoun with an antecedent of one first person, two second persons, one lower class and one upper class third person, and a female hamster. We could say all that in our sentence to be explicitly, but the pronoun-handling part of our brain probably just isn't advanced enough to understand this concept.
How do we know whether or not a proposed class of pronoun is biologically capable of being understood? One good indicator is the presence or absence of that pronoun type in any natural language. If no natural language has ever come up with a word with a specific, precise use, it's probably the case that such a use can't be conceived of pronominally. Humans are really creative when it comes to making up new linguistic forms. If we haven't done it in 6000 attempts, it's highly unlikely it can be done.
Second person clusivity is one of those things that has never been done. Your argument hinges upon second person clusivity. Paul is including himself, "I," and the Corinthians, "you," together in his "we." You're suggesting that that second person "you" consists of "you, the audience I'm writing to, the Corinthian Christians," and "other people who were with you at the time." That's second person clusivity - indication through a pronoun that both the second and third person are being implied. It's doubtful that this can be expressed. So the reason you're hearing "all the world" in "we" in I Cor 15 has to be your prior commitment to general redemption, and your expectation to hear salvific language used of all the world. It can't be due to Paul's word choice.
