The major misunderstanding is when the word, Apostle, is applied to Paul. There are only Twelve Apostles with the honor of having their names on the twelve foundations of the New Jerusalem, and of course, Paul is not one of them.
Apostle may be translated as "sente out." If the accounts of Paul's conversion are true, and I believe them, he is definitely sent out, and therefore he is an apostle in the sense of themeaning of the word.
His teaching seem completely sound, though many who read him misconstrue his teachings not being truly aware of the reason for them to the varied assemblies. This is easily rememdied by learning directly from Jesus Christ, Yeshua, as we are all invited byu Him to do.
Most read the Epistles as though they are of the assemblies witht he problems being addressed by Paul. Paul's teaching is he same as that of Jesus Christ, as Paul declares when he tells us his teaching is the one gospel, the oly gospel, that being of Jesus Christ.
If Paul seems offish at times, look for your current question's response from Jesus, Himself. You have been invited to share in this gift directly from God........I do it; oh, I also learn from Paul...God bless you and hold you close always.