
Think you have a great start. Don't know if I'm an expert (given my run of Brisket scores this year) but our friends like our stuff.
For me, Pepper is a KEY to Texas briskets. A more tranditional rub might cut your pepper to 1/4 cup
I like more onion power
1/4 c of garlic "might" be much, but it depens on the brand and how much you like it. I like granulated garlic, it holds up better, powder seems to loose it punch
One thing missing is sugar. I like to add about 1/2 cup of brown sugar to the rub. You can dry it first or just use the Brownulated Sugar.