Yet Paul was not appointed by the disciples. And this is crucial to understand in that it shows God can and does choose who He wants to be in the ministry.
But his ministry had to be recognized by the other apostles in order for it to be known by the Church. Otherwise anyone could claim that they were chosen directly by God. Do you claim that anyone after Paul was chosen by God and speaks with the authority of an apostle? Nor does the example of Paul take away from the fact that there were those who were chosen and commissioned by the apostles. Paul himself did this with Timothy and Titus, and instructed Titus to do the same. How can you claim that this line of commissioning shown in the Bible has come to an end?