The Catholic Church does not teach that we merit our sanctification; it is a pure grace. To bring up this charge is unworthy of honest discourse.
We were washed, sanctified and justified in the name of the Lord Jesus Christ and in the Spirit of our God.
If we are sanctified then we are made actually holy, not just imputed with holiness as a legalistic fiction. Are all those Protestants who have faith truly holy, i.e. reflecting the love of God and free from all attachments to sin and selfishness? If not, then "may the one who began a good work in you continue to complete it until the day of Christ Jesus."
No man may be able to boast in His presence, it is all because of grace.
Catholics also believe that it all because of grace. So where would anyone be able to boast?
Did you forget that you said, "Concerned only with our legalistic justification, Protestantism fails to recognize the greater mission of Jesus Christ, our sanctification."? Would you like to explain how we cooperate with grace, "reflect the love of God" and free ourselves "from all attachments to sin and selfishness" so that we merit the beatific vision and it NOT be by our own efforts and works? It seems like Catholicism likes to use lots of flowery, intellectual-sounding words and phrases to surround her doctrines when the simple and clear words of Scripture answer our deepest needs much better.
There IS no such thing as our holiness being a "legalistic fiction", it is a truth well laid out in Scripture that we are imputed with the righteousness of Christ, and not our own, is the only reason why we are saved.
What shall we say then that Abraham our father, as pertaining to the flesh, hath found? For if Abraham were justified by works, he hath whereof to glory; but not before God. For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness. Now to him that worketh is the reward not reckoned of grace, but of debt. But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness. Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works, Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered. Blessed is the man to whom the Lord will not impute sin. Cometh this blessedness then upon the circumcision only, or upon the uncircumcision also? for we say that faith was reckoned to Abraham for righteousness. How was it then reckoned? when he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision. And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also: And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised. (Romans 4:1-12)
And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith: That I may know him, and the power of his resurrection, and the fellowship of his sufferings, being made conformable unto his death (Philippians 3:9,10)