Skimming over the OP , I found that there is a misrepresentation of the word “we” in I John.
The word “we” as use all throughout the writings of 1John never relates to the Gnostic teachers but the believers. Apostle John is nowhere to exclude himself in this “we” being among many eyewitnesses to the “Word of life.” The theme of 1 John is fellowship and he is writing to the believers to combat specific threat to that fellowship which may influence some and may cause sorrow in the church so that John wrote that their “…joy may be full.”
1 John 1:4 And these things write we unto you, that your joy may be full.
The threat is the Gnostic movement prevalent during the time of Apostle John. Context -preceding verses, the following chapters, the whole book of I John “we” is being referred to believers. Similar assertion for the use of the word “we” is also found in Galatian 1:8 where Paul is battling Legalism.
Galatians 1:8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
Gnostic teachers are describes by Apostle John as follows:
a. seducers
1 John 2:26 “These things have I written unto you concerning them that seduce you.”
b. anti-Christ (against the teaching of Christ)
I John 2:18 “Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.”
c. Liars
1 John 2:22 Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son.
d. Deceivers
1 John 3:7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.
e. spirit of anti Christ
1 John 4:3 And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
f. worldly teachers
1 John 4:5 They are of the world: therefore speak they of the world, and the world heareth them.
g. spirit of error
1 john 4:6 We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.
Further, Apostle John used the word “they” in 1 John 2:19, rather than using the word “we” in reference to the Gnostics.
“They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.”