Paul is worthy according to his calling by God (hypothetically speaking, of course) to have such a role. I hear what you're saying, though. Even focusing solely on Jesus, his teachings and his life, the role of the Holy Spirit in our life is evidenced quite well as being, at the absolute very least, essential. Perhaps Jesus didn't go deep into the theological underpinnings because He was aware of the plan and knew that God would appoint others to cover these things in due time? Anyways:
“If you love me, keep my commands. 16 And I will ask the Father, and he will give you another advocate to help you and be with you forever— 17 the Spirit of truth. The world cannot accept him, because it neither sees him nor knows him. But you know him, for he lives with you and will be[c] in you."
“All this I have spoken while still with you. 26 But the Advocate, the Holy Spirit, whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you."
"“The Spirit of the Lord is on me,
because he has anointed me
to proclaim good news to the poor.
He has sent me to proclaim freedom for the prisoners
and recovery of sight for the blind,
to set the oppressed free,
19 to proclaim the year of the Lord’s favor.”[f]"
It's late and I can't form all of this all that coherently, but Jesus' entire ministry was enabled and preceded by the Holy Spirit's work. He preached and prophesied of it's role for his followers. He spoke of His (the Spirit's) role as being a helper, a teacher, an advocate, etc. He claimed that only His followers would know and accept the Spirit. It doesn't quite get to the level of monotonous detail of Paul's letters, but it lays the consistent groundwork that I would very confidently believe the Spirit himself built upon through inspiring Paul and the other apostles, along with other prominent followers henceforth.
I am aware of Paul's resume. But what sets Paul apart from Joseph Smith, who was also called by God?