I have come to the conclusion that the most powerful apologetics argument that a Catholic can make against Protestantism is that their Sunday Liturgy is actually man-made and thus blatant idolatry. Let me explain this more.
The most important duty a human has, regardless even of whether they are a Christian or not, is to worship God. This should be - without a doubt - an obvious truth that everyone can agree upon. Given this, a person must not only worship God, they must do so properly, i.e., they must worship as God has instructed them to do. This means that Liturgy requires divine revelation, because otherwise the person is "worshiping" God based on what sounds good to their human mind...but there is a word for worshiping according to what sounds good to you: it's called idolatry. So the only way to escape idolatry is to worship according to how God has divinely revealed it. Which leads us to the key problem which all Protestants face.
