Shieldbearer will help warrior get to turn 10 and is probably about the right time when your C'thun will have 10 attack, so can be used on curve often. Seems playable but also depends on other 7 drops. I can't really think of a 7 drop that would compete in a C'thun deck. The Obsidian guy will probably see play, might be preferred actually. Baron Geddon will still be likely, too. 10 Armor is 6 mana worth of stats. Seems good.
Servant is probably good, but easier to remove than Shredder. Borderline playable. Trades evenly with Yeti/Senjin, so not really OP imo.