In my experience, 205* is kinda magic if you have a known source of meat, sure it can be done anywhere between 195-215* but typically 205* is the sweet spot for the majority of briskets.
That said, you can make a very tender delicious brisket SV at 170* if you cook it long enough. The break down of connective tissue and collagen starts to happen at around 140* but it takes a long time to get there, days. At around 200* this break down starts to happen faster, but it’s a window of temp. Go to 225 IT and you have mushy meat. Pull at 190* and it may be dry and chewy. This is why we probe for tenderness and don’t get consumed with IT. Franklin knows this as well, but says he pulls the meat at 203*. My view is that he does this for safety of not over cooking, then in that cool down/holding process the collagen dissolves and the connective tissue breaks down from a high of 203* to final hold of 140*. The meat shouldn’t mush in that time and temp, but will be super tender and juicy. It’s all time with temperature. It’s not rocket science.