The writer is trying to emphasize the large crowds that are going out to hear John’s preaching and to be baptized by him. In the case of Paul’s statements in Romans, prior to his “all,” he has already made the case that both Jews and Gentiles are under sin and that no man may be justified through the law, because the law reveals sin, and that the world is shut up before God and must acknowledge their sin. Now what, in the case of Paul, indicates he is really saying “only some have sinned and fallen short of the glory of God”?
The word “have” and tenses in the word sin. If he had said “all have sin”
I could make a case for your literal claim of the use
of “all”.
But because he said “All have sinned” this indicates
that all have actually already actualized a sin, committed
such rather than inherited, and even you have agreed
there are too many instances in which that just
does not appear to be true such as the Downs baby.
The only way for the phrase to even begin to be
sensible for most people would be to
change “all” to more of the Greek pas of “most” or just about everyone.
Or to drop the past tense on sinned.
If it said Most have sinned. Yes that’s entirely likely in the
literal sense.
Or if it said “all have sin” then yes literal makes sense.
But literally “all have sinned”? No not in the literal
sense.