The expression is not the issue. It is a misunderstanding of what Saint Paul says to Timothy and what most Christians really mean by saying they have "faith in Jesus Christ". Without out a broader understanding of other Christians beliefs and what they really mean by that statement, am not sure how one can so quickly condemn them for saying just that. And twisting words around to attempt to make the verse say something else is not helping others understand what the point/problem is with a simple statement about faith.
Many Christians, including Catholics, hold salvation to be a matter not completely settled until the end of this life. So with those Christians it is not usually a single act, (like the thief on the cross), but a complete and ongoing process of God (and others) helping to lead someone arriving in Heaven when this life is over. But even those saying simply that all they need to do is confess a genuine "faith" that Jesus Christ has "saved" them or that they have "faith in Jesus", when pressed will often admit it is not really that simple. We all need God's help (Grace) and we all also need each other's help to safely make it to Heaven.
For Catholics and many other Christians, it is also true that we believe even our faith is a gift from God. That belief excludes the whole notion that seems to trouble you about this verse and the way many of us use it, because even our faith is from God.
Having a "faith in Christ" is the believer acknowledging (and Saint Paul acknowledging that for Timothy) the first step has already occurred with God's help (the Spirit moved them to respond to His call) and this could be said by all Christians. This gift of faith from God is just the first baby step in our life's journey and our hope for salvation.
Don't believe me that this is what I believe 2 Tim 3:15 means or what I mean when I say our salvation starts with faith in Jesus. Fine. Then believe the teachings I will not stop following, the testimony of thousands of years of witness to the faith and recorded in the Catechism backs me up as being what all Catholics should believe about our "faith".
179 Faith is a supernatural gift from God. In order to believe, man needs the interior helps of the Holy Spirit.
Catechism of the Catholic Church - PART 1 SECTION 1 CHAPTER 3 ARTICLE 2
166 " Faith is a personal act - the free response of the human person to the initiative of God who reveals himself."