The OP concerns God given faith and whether or not it can be defective.
My concern is not primarily with personalities (but they must of necessity be involved to some degree).
Right now I would like to address this issue apart from the writings of these men (as much as possible).
Faith that is given by God can in no way be defective.
However, I believe the Scripture teaches that of those with this God given faith many indeed do come short of the perfection of this faith.
Perfection means complete, mature but not sinless perfection.
Though it is the will of God that we do not sin.
1 John 2:1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
Yet even within this desire expressed by the Spirit of God through the Apostle John is the advocacy of Jesus Christ as our intercessor.
There is Scripture which speaks of carnal Christians.
First the Corinthian believers are called sanctified saints…
1 Corinthians 1:1 Paul, called to be an apostle of Jesus Christ through the will of God, and Sosthenes our brother,
2 Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints, with all that in every place call upon the name of Jesus Christ our Lord, both theirs and ours:
Later they are rebuked for their carnality.
1 Corinthians 3:1 And I, brethren, could not speak unto you as unto spiritual, but as unto carnal, even as unto babes in Christ.
2 I have fed you with milk, and not with meat: for hitherto ye were not able to bear it, neither yet now are ye able.
3 For ye are yet carnal: for whereas there is among you envying, and strife, and divisions, are ye not carnal, and walk as men?
4 For while one saith, I am of Paul; and another, I am of Apollos; are ye not carnal?
In another place they are warned about the repercussions of eating the Lord’s Supper in an unworthy manner (for instance coming to communion while drunk).
1 Corinthians 11
27 Wherefore whosoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord.
28 But let a man examine himself, and so let him eat of that bread, and drink of that cup.
29 For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body.
30 For this cause many are weak and sickly among you, and many sleep.
31 For if we would judge ourselves, we should not be judged.
32 But when we are judged, we are chastened of the Lord, that we should not be condemned with the world.
Just how far can things get out of hand before the Lord lets loose the chastisement?
Revelation 2
20 Notwithstanding I have a few things against thee, because thou sufferest that woman Jezebel, which calleth herself a prophetess, to teach and to seduce my servants to commit fornication, and to eat things sacrificed unto idols.
21 And I gave her space to repent of her fornication; and she repented not.
22 Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds.
23 And I will kill her children with death; and all the churches shall know that I am he which searcheth the reins and hearts: and I will give unto every one of you according to your works.
Now I am certainly not saying that a Christian can get away with committing fornication or going back into the bondage of sin. Obviously we cannot and may even be taken home for the evil done in the body.
But the scriptural evidence is that Christians are indeed capable of being carnal and have the ability to do some terribly evil things.
After justification comes sanctification to mortify/crucify the flesh from whence comes carnality which appears to be the condition of “babes in Christ”
Sanctification is a life long endeavor.
So, while God’s gift of faith through grace is perfect and in no wise defective in that it brings with it eternal life, the requirement of sanctification through faith is not always attained to a high degree in the believer and he/she can even be a miserable failure in this area.
1 Corinthians 3
10 According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon.
11 For other foundation can no man lay than that is laid, which is Jesus Christ.
12 Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;
13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
14 If any man's work abide which he hath built thereupon, he shall receive a reward.
15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
16 Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
The key is the foundation that no man can lay than that is laid which is Jesus Christ.
He is the author and finisher of our faith.
We build upon that faith which brings the absolute promise of eternal life.
In that it cannot be defective ("I give unto them eternal life and they shall never perish").
But as to the rewards of gold, silver, precious stones, wood, hay stuble, some receive a reward,
some lose all yet they themselves are saved.
HankD