Possibly no recognized worldly concept of a leader applies to any such men described in the NT, and this could be due to the fact that elders always functioned in unison with one another: You never find one man standing up declaring, “I am the leader!“
Sometimes it seemed as if Peter was the “leader”, then James, then Paul: it was a dynamic, fluid thing, where God’s wisdom for a particular matter could come thru any of the elders.