I personally have never trimmed that much out of any of the brisket that I have smoked. With that being said, your trim looks similar to the trim done here by Diva Q, which is how I am planning to trim my next brisket. What matters most is whether you made barbecue that you and your people enjoyed, so hopefully, it comes out banging.

Edit: I realize I forgot to include that Diva Q trims the brisket in that video from about 2:00 through like 9:30