You are conflating two entirely different issues - which Protestants are wont to do with those issues.Of course they do. Often they hold to the heretical belief "Once Saved, Always Saved" and sometimes the predestination theory of the "elect" and in those odd heresies the "actual" Church is simply those who are saved. That is why some of them grudgingly "admit" some Catholics may be "saved".
They also misunderstand the hierarchy of worship, having rejected the highest form of Worship, the Holy Sacrifice of the Mass, they conflate intercessory prayers TO the Saints and Mary as if we were praying to them as Gods. Since, in their heretical world, worship and prayer are the same, they cannot imagine why we hold to the ancient and Traditional beliefs given to us by Our Lord and His Apostles and the Apostolic Succession.
That is an excellent point. OSAS is a flawed Protestant doctrine built upon the errors of Rome's Palegius heresy. Unfortunately, as you rightfully point out, many Protestants have fallen for this grievous error. I would point our Protestant brethren to the following confession:
Of the Perseverance of the Saints
I. They, whom God has accepted in His Beloved, effectually called, and sanctified by His Spirit, can neither totally nor finally fall away from the state of grace, but shall certainly persevere therein to the end, and be eternally saved.[1]
II. This perseverance of the saints depends not upon their own free will, but upon the immutability of the decree of election, flowing from the free and unchangeable love of God the Father;[2] upon the efficacy of the merit and intercession of Jesus Christ,[3] the abiding of the Spirit, and of the seed of God within them,[4] and the nature of the covenant of grace:[5] from all which arises also the certainty and infallibility thereof.[6]
III. Nevertheless, they may, through the temptations of Satan and of the world, the prevalency of corruption remaining in them, and the neglect of the means of their preservation, fall into grievous sins;[7] and, for a time, continue therein:[8] whereby they incur God's displeasure,[9] and grieve His Holy Spirit,[10] come to be deprived of some measure of their graces and comforts,[11] have their hearts hardened,[12] and their consciences wounded;[13] hurt and scandalize others,[14] and bring temporal judgments upon themselves.[15]
*Scripture footnotes at reference
Westminster Confession of Faith-Preseverance of the Saints
Most Protestants understand these principles although they have their doctrine skewed by years of listening to Rome's work based errors. Feeling people need to go to confession, take grace, do penitence, pray the Rosary, etc., is nothing more than reducing Christianity down to religion with ceremonial steps to achieve the goal of salvation.
This was certainly not the view given to us by Our Lord.