And ... Jesus said that such wasn't to be in His church ...
In your verses from Mark, Jesus is not telling the Apostles that they would not rule, but they would not rule LIKE THE GENTILES. In other words, the leader would serve, just as Jesus washed the feet of His disciples. Leadership with humility does not do away with authoritative leadership.
So that you may see the context, here are SOME quotes from St. Chrysostom...
"And if anyone would say 'How did James receive the chair of Jerusalem?", I would reply that he appointed Peter a teacher not of the chair, but of the world..." (Chrysostom, on John, Homily 88, Migne PG 59:478, Giles page 164)
"...The merciful God is wont to give this honor to his servants, that by their grace others may acquire salvation; as was agreed by the blessed Paul, that teacher of the world who emitted the rays of his teaching everywhere." (Chrysostom, on Genesis, Homily 24, Migne PG 53:211, Giles page 165)
"Peter, therefore, turning seeth the disciple whom Jesus loved, who also reclined on His breast at supper, following, and saith: 'Lord, what shall this man do?' Why did he mention the reclining? Not without reason or by chance, but to show what confidence Peter had after his fall. For he who then had not dared to ask a question, but committed it to another, was given the presidency over the brethren. And he not only commits his own case to another, but even himself puts a question to the Master about another, and John this time is silent, while it is Peter who speaks....Peter loved John greatly...Since then He foretold great things for Peter, and entrusted him with the world, and predicted his martyrdom and testified that his love was greater than that of the others, Peter wishing to receive John as his fellow, saith: And what of this man? Shall he not go the same way?"
Note, this is from an Eastern Archbishop of Constantinople from c. 400AD
Brother in Christ
"Peter, therefore, turning seeth the disciple whom Jesus loved, who also reclined on His breast at supper, following, and saith: 'Lord, what shall this man do?' Why did he mention the reclining? Not without reason or by chance, but to show what confidence Peter had after his fall. For he who then had not dared to ask a question, but committed it to another, was given the presidency over the brethren. And he not only commits his own case to another, but even himself puts a question to the Master about another, and John this time is silent, while it is Peter who speaks....Peter loved John greatly...Since then He foretold great things for Peter, and entrusted him with the world, and predicted his martyrdom and testified that his love was greater than that of the others, Peter wishing to receive John as his fellow, saith: And what of this man? Shall he not go the same way?"
This is actually quite an interesting passage.
Per my reading ... after Jesus reconforms Peter's love for Him ... and assigns him the task of feeding His lambs/sheep, ... Peter inquires of the Lord as to what John is to do.
Seemingly, ... Jesus answer to Peter is that ... what John is to do is not his business ... and that he (Peter) should attend to the task of following Him.John 21:20 Then Peter, turning about, seeth the disciple whom Jesus loved following; (which also leaned on his breast at supper, and said, Lord, which is he that betrayeth thee?)
21 Peter seeing him saith to Jesus, Lord, and what shall this man do?
22 Jesus saith unto him, If I will that he tarry till I come, what is that to thee? follow thou me.