Were we all capable of the worst sins even if we never committed them?
Yes. Romans shows that every one of us was nothing but a hell-bound, filthy, wicked sinner, whether we actually did any of the things listed or whether we did not. Potentially, all were capable of going to the very depths of sin. That is the diagnosis Romans gives.
Les explains that the letter to the Romans was written to show that we were nothing but hell-bound, filthy, wicked sinners—every one of us—whether we actually did any of the things listed or whether we did not. Even if we never committed them, potentially we were all capable of going to the very depths of sin. That is what Romans shows. Then Romans gives the remedy: the Gospel—that Christ has already forgiven us, already died for us, and His blood has already paid the payment, and all we have to do to appropriate it is believe it. Ephesians then hammers home our position in Christ, in the body, with its roots in verse 3, and asks where we are now positioned: in the heavenlies. We are not an earthly people but a heavenly people, even though we are on the earth.