In regard to Hebrews 10:26, to "sin willfully" carries the idea of deliberate intention that is habitual, which stems from rejecting Christ deliberately. This is continuous action, a matter of practice. Now we don't walk along our daily life and "accidentally" fall into a pit called sin. We exercise our will but, the use of the participle clearly shows a ongoing, willful, habitual action.
The unrighteous practice sin (1 Corinthians 6:9-10; Galatians 5:19-21); not the righteous, who are born of God (1 Corinthians 6:11; 1 John 3:9). *Hermeneutics. These Hebrews who wilfully sin after receiving the knowledge of the truth were not saved but instead rejected the truth with eyes wide open.
The writer nowhere makes that distinction that they were not saved... that is your eisegesis.