But does it follow Sanderson's first law of magic?
An author’s ability to solve conflict with magic is DIRECTLY PROPORTIONAL to how well the reader understands said magic

That's a misunderstanding of the first law. The first law is to prevent authors from never explaining anything, using the excuse "they did magic" in place of an explanation. The first law states that you have to have well defined rules for your magic, and that your solutions must follow those rules. It does not say that you must understand all of those rules the very first time that you see that magic.

Did you know what allomancy was the very first time kelsier decided to just eat tin and "burn" it? Of course not; you got bits and pieces of the rules as you continued to see more allomancy, eventually arriving at a near complete understanding of all its rules by the very end of the book. But the very first time kelsier used allomancy, you had absolutely no warning he was going to do that, and no understanding of the rules in place that allowed him to burn a metal in his stomach so that he could hear better.

What vin did is the very first time you have witnessed something very different than allomancy. A true Deus Ex Machina is never explained, or worse, explained as a very fortunate fluke. But what vin did is a cornerstone of the entire cosmere, and over the course of the next books, you'll begin to encounter more rules naturally over time -- as you did with allomancy -- until you arrive at a near complete understanding of the entire cosmere