You are correct that its undercooked. These guys are correct that it should be probe tender.
Unless your cooking competition i would NEVER trim that aggresively. You removed much of the flavor and the fat aids in moisture retention.
Looks like its cut just fine.
Practice, practice, practice.
And try the KISS principal when cooking brisket until you master it THEN you can add all that other crap.
Pitmaster @ Lockharts BBQ
I cook the best brisket north of Dallas. Get over it.
Northern midwest director for OBR