Well sir, whoever compiled the books saw fit to include the passage from Mark, and this one as well, from Luke 22:31,32...
“And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat: But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren.”
The Lord just made it clear right there, that even after the disciples ate the bread, and drank of the cup (verses 19 and 20), they were not yet converted. The conversions would happen after the Lord ascended, for the Holy Ghost would not come until the Lord physically departed. (John 16:7)
By your lights Paul, the early Church fathers, saints, martyrs, theologians, scholars, all got it wrong in believing the literal terms of Eucharistic consecration.
A sign of the reality of Presence of Christ in the Eucharist may be seen in what St. Paul wrote to the Corinthians, in which he not only repeated the words and actions of the Last Supper but notes the punishment upon those who unworthily receive the Holy Eucharist:
11:23 For I received from the Lord what I also delivered to you, that the Lord Jesus on the night when he was betrayed took bread, 11:24 and when he had given thanks, he broke it, and said, “This is my body which is for you. Do this in remembrance of me.” 11:25 In the same way also the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.” 11:26 For as often as you eat this bread and drink the cup, you proclaim the Lord’s death until he comes. 11:27 Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. 11:28 Let a man examine himself, and so eat of the bread and drink of the cup. 11:29 For any one who eats and drinks without discerning the body eats and drinks judgment upon himself.