THE first thing you Farked up is> removing the the fat. Fat it keeps the meat moist and adds flavor and bastes the brisket as it cooks.
THE second thing you Farked up> cooking it at such a low temp. Flats do best from 250-275
THE third thing you Farked up> is not paying attention so for your benefit I'll kick the dead pony one more time, "YOU CAN NOT COOK GREAT BBQ BY COOKING IT TO AN INTERNAL TEMP OR BY COOKING BY XXX MIN PER LB." Probe tender is the only reliable method to ensure the proper time to pull for maximum tenderness"!
I'm a Proxy Vegetarian> Cows eat grass & I eat cows.