Out of context, dude. Paul was talking about those in Corinth who were saying "I belong to Paul ; I belong to Cephas; I belong to Apollos; I belong to Christ."
Regardless, the principle transcends the immediate application, like as does " it is accepted according to that a man hath, and not according to that he hath not," though its application here is about giving, "For if there be first a willing mind, it is accepted according to that a man hath, and not according to that he hath not." (2 Corinthians 8:12) "For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more." (Luke 12:48)
Moreover, thinking and exalting mortal Mary way beyond what which the holy Spirit reveals of her in His word (who says far more of Paul and His labors) is indeed divisive, and thus you have your Catholic Marian movements and societies which further divide Bible Christians from Catholicism.
You're acting as though 2 Corinthians 8 automatically is relevant 1 Corinthians 3 - 4; or that Luke 12 has to do with it.
For your 2nd paragraph, as an old tutor of mine used to say, "Close, but no dog biscuit."
The difficulty in discussing any such issues, is that most people who are deeply engaged in these topics have certain verbal formulations burned into their head -- both for what they believe to be true, and therefore hold fast to; and for what they consider to be the errors of others.
What can happen all too often, is that a person says "statement XYZ" then another person hears the part "X" and mentally rushes in to fill in "XAB" instead -- which isn't what the first person said at all.
The problem is that I reject the insistence on Sola Scriptura -- "If it wasn't mentioned in the Scriptures, it is not necessary for salvation" can too easily become "if it wasn't mentioned in the Scriptures, it simply is forbidden to consider that it might happen to be of God or used by God to help someone towards Salvation".
And THAT last sentence too often springs the knee-jerk counter argument that "once you go outside the Scriptures, you open yourselves up to all KINDS of errors and even demonic influence"...which then auto-catalyzes into "everything not explicitly mentioned in Scripture (especially the teachings of my specific denomination" is *perforce* demonic.
The problem is that you are insisting that anything not listed in Scripture MUST be completely false; that's a good way to eliminate a LOT of errors, but you might be throwing some Grace away too. Mary is not salvific as Jesus is, she didn't die for our sins; but by His grace, I believe He allows His Mother to be a channel of God's Grace and Power.(*)
There's a difference between "a necessary and required component of the mechanism of salvation of mankind" and "God allows His Mother to act to spread God's grace to help certain individuals and by the way, since God is so merciful, and not-hung-up-on-Protestant-doctrine, that as many people want to approach Him that way, or grow in faith that way, He will accept them instead of casting them aside due to lack of ideololgical purity"
(*) As it turns out, there are Catholic teachings which go much further than that, based on certain Scriptures which are not emphasized by Protestants. And on the other hand, the Lutherans retained the feast of the Assumption of Mary even though it is not in Scripture.