According to the very first proposed declaration discussed by the Georgia secession convention, tariffs weren't the issue that caused alarm:
"The State of Georgia is attached to the Union, and desires to preserve it, if it can be done consistent with her rights and safety; but existing circumstances admonish her of danger: that danger arises from the assaults that are made upon the institution of domestic slavery, and is common to all the Southern States."
That's danger from assaults on slavery, not from Republican tariffs.
I found a link to the proceedings of that Georgia meeting and didn't see any concern with tariffs. But I admit that I wasn't looking too hard or expecting to find it. Maybe somebody can find a preoccupation with tariffs that matches the worry about slavery expressed in the above quote.
Cherry-picking your quotes again, are you?
Well, here's a quote -- addressed to Georgia and all the Southern States.
The Southern States now stand in the same relation toward the Northern States, in the vital matter of taxation, that our ancestors stood toward the people of Great Britain. They are in a minority in Congress. Their representation in Congress is useless to protect them against unjust taxation, and they are taxed by the people of the North for their benefit exactly as the people of Great Britain taxed our ancestors in the British Parliament for their benefit. For the last forty years the taxes laid by the Congress of the United States have been laid with a view of subserving the interests of the North. The people of the South have been taxed by duties on imports not for revenue, but for an object inconsistent with revenue -- to promote, by prohibitions, Northern interests in the productions of their mines and manufactures. [Emphasis added.]
--Robert Rhett, "South Carolina's Address to the Slaveholding States" (1860)
Oh, yeah, and he talked about slavery, too -- since the Northern politicians had put slavery on the agenda, politically and rhetorically.
Not even Lincoln had talked about slavery, before 1854, the way he did afterward. But after that time, he talked about it, and the freesoil Whigs talked about it, and the Republicans talked about it, incessantly.
So the mantra, "it was all about slavery," belongs rather to the Northern politicians like Lincoln, and even then only to their public platforms and position papers on the subject, and it is not descriptive of their legislative effort as a whole, or of their relationship as a whole to the body of Southern opinion. It was one element in a grand strategy of national domination, one that the South confronted by leaving the Union.