Does Romans teach that everyone was capable of deep sin even if they didn't do certain things?
Yes. Romans shows that every person was a hell-bound, filthy, wicked sinner, regardless of whether they actually committed the listed sins. Potentially, all were capable of going to the very depths of sin. The letter then presents the Gospel remedy: Christ has forgiven, died, and paid the payment for those who believe.
Les explains that the whole idea of Romans was 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. Potentially, all were capable of going to the very depths of sin. That is what Romans shows. The remedy is the Gospel: Christ has already forgiven us, already died for us, and His blood has already paid the payment. All we must do to appropriate it is believe it. Les says Romans is doctrinal and basic, unlike Corinthians, which reproved problems, and Galatians, which corrected a return to legalism. Ephesians instead hammers home the believer’s position in Christ and in the heavenlies.