Typically I say play what you like, but already I don't expect much out of a level 30 shield ogryn, let alone a low level ogryn with even weaker damage output.

Been leveling up another vet on heresy and had this level ~20 shield ogryn blocking the only path with a ton of shooters on the other side. Couldn't shoot through him since the path was too narrow. I attempted to let him know that we can't shoot through him, but just then a bomber dropped a grenade at his feet and he and another guy that was trying to go through him went down. They both quit after that.

Rarely have I played with decent shield ogryns, but typically they either plant, or knock down the enemies without killing them, so I can't get headshots or cleave. Then I have to run around checking every body to see if they are still alive. It's like the shield is made to actively work against the team.