You're right, how else can anyone have an opinion if Ross Brawn says it's worrying? I mean what else is the MD of F1 going to say in the heat of the moment?
A barrier on a straight is designed to behave very differently from a corner, especially one which is covering an exit/entrance from a Marshall post to the circuit. The fact the post in the picture has retained it's connection to the ground and has bent on impact, shows that the barrier did it's job. So much that Grosjean didn't end up in the dirt behind the barrier like this wheel did. I assume you have the same view on the tyre tethers as you do on the barriers?
Exactly, even the most strongest of materials have a breaking point. The barrier actually held onto the safety cell, which is the key point to remember. The balance is if you make the car to be further stronger there will be higher impact forces on the drivers. A car shedding bits is dissipating kinetic energy; crushable structures to absorb energy while limiting maximum g loading are critical for safety. However taking a barrier on a straight as a ruling example for all barriers condition probably isn't the best place to start.