Why did Paul (who was extremely opposed to Christianity before his "conversion") have such massive influence over Christian Doctrine when he never actually met Jesus and only met Peter for 15 days?

Paul never met Jesus he only claimed to have a vision of him, and he met with Peter over the course of only 15 days. In addition to this before his conversion to Christianity he was openly one of the most hostile people to Jesus' teaching and message. When he converted he immediately tried to start dictating christian doctrine and introduced things such as but mot limited to:

• Concept of the Trinity in how it's viewed today
• Concept of Salvation through grace alone
• Rejection of Jewish law (when Jesus followed Jewish law)
• Gentile Inclusion (when before the thought was that Jesus only came to the Israelites)
• Changing the role of the Holy Spirit (from what it was in Judaism (Ruach HaKodesh) and making it a separate person in the Trinity)
• The theology surrounding the cross and resurrection
• The concept of "New Creation" and Transformation upon conversion
• And lots of topics around "End Times" prophecies

If Paul never existed Christianity would have been very different and would have basically looked like Ebionites https://en.wikipedia.org/wiki/Ebionites . Why was Paul not seen as a figure like Joseph Smith is seen? Or a con-man trying to do whatever he can to undermine Jesus message?