They believed themselves to be doing the work of the spirit. Yeshua made that point very clearly. He also said that he did not know them, so you are right, they were not cutting the mustard.
This is true of most that call themselves “Christian” today.
It's not a matter of losing salvation, because as Yeshua made clear in Matthew 24 that one must endure to the end to be saved.
The verses that you rely on do not offer what you want to believe they do. They only reflect the apostle's confidence in a particular congregation, not a guarantee of salvation.
Peter addresses this well
2Peter 1
[1] Simon Peter, a servant and an apostle of Jesus Christ, to them that have obtained like precious faith with us through the righteousness of God and our Saviour Jesus Christ:
[2] Grace and peace be multiplied unto you through the knowledge of God, and of Jesus our Lord,
[3] According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
[4] Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
[5] And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
[6] And to knowledge temperance; and to temperance patience; and to patience godliness;
[7] And to godliness brotherly kindness; and to brotherly kindness charity.
[8] For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.
[9] But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins.
[10] Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall:
Get that? - They had forgotten that their old sins were purged!
Practicing “lawlessness” means rejecting Torah, either consciously or unconsciously.
If we truly yield to him, he does write his laws on our hearts, but how many truly yield? Hebrews 6 and 1Peter 2 are not idle chit-chat. They address people that had the Holy Spirit, but failed.
Unless you natively speak and read Greek, the Greek is no key to anything. The English translations of Hebrews and 2Peter say it as it was meant to be said.
Good talking to you then.