Ah sorry, missed this in typing my earlier post.Why would Paul say Christ sent him not to baptize in I Corinthians if it's essential for salvation?
For me, that's a context issue. Back up to verse 10, which ironically implores the audience not to be divided. (Evidence God has a sense of humor.) He's talking about the human quality of identifying with the people preaching, rather than with Christ. Immediately prior to the verse you reference, he's rhetorically asking if he baptized people "in the name of Paul." He clearly was baptizing people, as he named them. In fact, he couldn't actually remember all the people he baptized in the area.
Then he says that he wasn't sent to baptize, but to preach. Which is probably true. We all have roles to play in accordance with God's plan.
But, at a fundamental level, I think there's more agreement here than otherwise. Your formulation of "not strictly necessary, but still needed" is one that I can agree with. Particularly in the sense that there's a risk of focusing - like those early congregations did - on a kind of checkbox mentality.