Sorry to be just getting back...had a series of snafus to deal with yesterday.
Your hang test results lead me to believe the flat was overdone, which is why it was on the dry side. An underdone flat would have produced similar results. Points are very forgiving, moisture wise, and almost always probe tender for me before the flat's ready. T
When I determine doneness, I take 3 things into account; 1. the feel or "jiiggle" of the whole packer, 2. internal temps and 3. probe test. I would replace what you're now using with some simple round wooden 6" (or longer) skewers. You'll find them at the grocery store, Walmart, etc. It's basically an oversized toothpick that allows you to push through from top to bottom anywhere on the brisket. When properly done, they WILL slide thru the point like butter. The flat will give some resistance but not much. Think of probing St Louis ribs, same thing.
While I've only smoked maybe a dozen or less Wagyu packers, I've found they they tend to come done a few degrees less than the usual 202 - 206 range. I think I had one done around 196. BTW, I always reference the temp at the dead center of aa packer, as point and end-of-flat temps tend to vary a bit.
I would suggest that in the future you hone your craft using a good Angus USDA Choice packer. Creekstone Farms is a good source. 13 - 15 lbs is a good weight range. Cook at 250 and count on 75 - 90 minutes @ pound, post-trim. I would keep the seasoning to S&P and forget injections until you're confident as per your results. Then, as Smokin'Okie used to say, make changes one at a time, if so compelled to make changes.
That all said, Cal has cooked truckloads of briskets so anything he says gets priority ;-) Good luck!! You'll get there ;-)