"For all have sinned and come short of the glory of God". Is Abel excluded?
There is context to the words you're referencing. Just like you're ignoring the fact that Paul clearly said that there men that did NOT sin like Adam sinned.
Rom 3:9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin;
Rom 3:10 As it is written, There is none righteous, no, not one:
Rom 3:11 There is none that understandeth, there is none that seeketh after God.
Rom 3:12 They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.
Paul is referencing Jews and Gentiles in Romans 3:9. He wasn't referencing Abel.
Read what God said about Abel.
Heb 11:4 By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous, God testifying of his gifts: and by it he being dead yet speaketh.
Prove the "all" that have sinned is a reference to all of humanity. It is all of a two kinds that are referenced. Jews and Gentiles.
We know Paul isn't talking about anyone else because Paul clearly states that the righteous have "gone out of the way". Which means, they once existed. Paul is referencing the continued downfall of men absent God.
Psa 14:2 The LORD looked down from heaven upon the children of men, to see if there were any that did understand, and seek God.
Psa 14:3 They are all gone aside, they are all together become filthy: there is none that doeth good, no, not one.
Sin so permeated mankind that the righteous ceased to exist among mankind.
Gen 6:5 And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
Gen 6:6 And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
The battle for humanity didn't center around Adam and Eve. It began there but it didn't end there. Abel was born innocent and we have ZERO examples of him ever sinning or acting contrary to the will of God.
So deal with it. Prove that Abel sinned. Go for it.
To be clear, Abel still didn't have the right to Eternal life. Your view does not deal with any of these facts.