This sounds more like Paul’s “Gospel” than Jesus Christ’s. There’s no guarantee that these un-Christian “Christians” will live a “defeated life” (whatever that may be) in this world.
If one is engaged in a truly righteous act, then it is never “self-righteousness”.
All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works.2 Tim 3:16-17.
Your reject God's Word to your peril.
Do you not believe that Paul wrote Scripture under the leading of the Holy Spirit?
Or do you think Paul just made up what he wrote and did so knowing that he was (allegedly) contradicting Jesus?
Paul's gospel IS Jesus Christ's gospel...That's where he got it from, for instruction to the churches...