You are trying to pit unclear scripture against clear. I agree that many will be surprised and that is because they did not believe what is clear. They deny sound doctrine. The Rev passage is not about an individual turning from God. It is speaking to a church that turned from its first love and is in danger of being removed.
If scripture is not enough then try and use some logic. There is no reason to warn a saved person if they could stray since the saved cannot lose their salvation. If they would die they would simply get a promotion making any warning in vain. Again the Rev passage is not about a straying Christian, but a church that has left its first love and in danger of being removed.
What is meant by first love has had many speculations, but for sure it is not about them living in sin. 1John 3:9. Most likely it is about them becoming a social club more then a church spreading the gospel.
so there was a whole church full of believers who had turned from their first love.
Ephesians 4: 17 This I say therefore, and testify in the Lord, that ye henceforth walk not as other Gentiles walk, in the vanity of their mind,
18Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:
19Who being past feeling have given themselves over unto lasciviousness, to work all uncleanness with greediness.
20But ye have not so learned Christ;
21If so be that ye have heard him, and have been taught by him, as the truth is in Jesus:
22That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts;
23And be renewed in the spirit of your mind;
24And that ye put on the new man, which after God is created in righteousness and true holiness.
25Wherefore putting away lying, speak every man truth with his neighbour: for we are members one of another.
26Be ye angry, and sin not: let not the sun go down upon your wrath:
27Neither give place to the devil.
28Let him that stole steal no more: but rather let him labour, working with his hands the thing which is good, that he may have to give to him that needeth.
29Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
30And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
31Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:
32And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.
Warning to believers not to fall back into a walk as in the past. Note to walk verse 22 "That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts;" The old man the Old Sinful man (i.e the old sin nature).
Ephesians 5: 16 Redeeming the time, because the days are evil.
17Wherefore be ye not unwise, but understanding what the will of the Lord is.
18And be not drunk with wine, wherein is excess; but be filled with the Spirit;
Be wise not unwise walk under the control of the Holy Spirit not under the influence of anything else.
1 timothy 4:1 Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils;
"Some being believers will depart from the faith. They will be seduced by spirits and doctrines of devils"
2 Speaking lies in hypocrisy; having their conscience seared with a hot iron;
3 Forbidding to marry, and commanding to abstain from meats, which God hath created to be received with thanksgiving of them which believe and know the truth.
4 For every creature of God is good, and nothing to be refused, if it be received with thanksgiving:
5 For it is sanctified by the word of God and prayer.
Very clearly Paul says believers can walk away from service and return to sin.
And of course 1 Corinthians 3 Paul says he must speak to them as carnal, out of God's will out of fellowship and following false doctrine.