Sentinel's caste was pretty much built to take hits like what Starscream is delivering and Sentinel himself is pretty hardy, though if Starscream would stop and look he'd realise he's done a substantial amount of damage.

"Never to a Decepticon!"

Okay maybe he couldn't keep a shitty one liner off forever, but it's probably a good thing for Starscream this shitty golden monstrosity is no longer sticking to full sentences anymore? Stick around, maybe you'll see him puke up some energon. Delicious.