It's more verbal the less general it is, and it's very particular. So one cannot dismiss the verbal force as you have.Actually, it is ἄνθρωπος Χριστὸς Ἰησοῦς; you cannot detach ἄνθρωπος from Χριστὸς Ἰησοῦς. They are all nominative nouns.
"it is rendered "gave" because it is an aorist, not a present tense verb. As Wallace points out, it never completely loses its verb function, but it does not act as a regular verb. You are diminishing the adjetival function, if not erasing it completely to make it function the way you want it to function. If it is an adjective, then the primary function is as an adjective, not a natural verb.
Also, it's not an adjective. It's a participle. It's also not functioning as an adjective in any translation I have seen.
But that's not my evidence against your view. It's what happens to the syntax when one adds the same verb from 1 Ti 2:5ab.
If έστιν is added to ἄνθρωπος Χριστὸς Ἰησοῦς it becomes a predicate nominative and results in:
Christ Jesus [is] the man who gave himself....
But that becomes a separate sentence and not a dependent clause.
You described how you view the verse in a fuzzy way but you have not parsed it with your addition. Doing that shows it's not a possibility, at least it's not how any English bible renders it.