Don

I do not think it is not really possible to be counterfactual about Spiritual things, as God is certainly in control.

We know Peter wrote that what Paul wrote was Scripture and that endorsement is good enough for me, Peter being one of the 3 that are one of the 12.  The apostles also endorsed Paul as being apostle to the gentiles, which was something like 98% “market share” of the people of the 1st century, so no wonder we find Paul having a huge influence.  And with the resulting gentilization of the church, his letters go to the front of the line in the Bible once they are no longer scrolls in a basket but a codex (book form).

I do not see any such term as secondary apostles in the Bible, there a some people who are simply called apostles, they include the 12 and some others.  Such people (apostles) can exist today, but we often call them missionaries.