If Paul wanted to refer to pistis (“faith”), he could have written the feminine haute, instead of the neuter touto, and his meaning would have been clear.
Given the entirety of scripture where Abraham was justified by faith it really seems illogical that God gives what He requires.
As well,
Romans 6:23
For the payoff of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
So while we can dig down to the grammar, and there may be some room for debate, it still has to align with the entire Gospel message.
The gift in Eph. 4:8 is salvation. Salvation (being saved), is our justification, righteousness and eternal life gifted to us by God by His grace, on account of our faith
So you think God giving his only begotten Son to this world is illogical, since the Son did everything all the time in all circumstances that His Father required of humanity?