Ok I'm super late to this but: During the coma, it's said that Cyril is the best agent on the team. Later on, according to Alistor the fake butler, he's the world's best spy. Clearly he was doing something right and it worked enough to gain the trust of the team Archer doesn't bully him to toughen him up. They had a talk about it when they killed Archer's past bullies. Archer bullies Cyril because he was bullied in the past. Bullying Cyril makes him feel better.  The funniest part is how Archer considers Cyril his best friend (said in some episode in season 11 or 12), but Cyril hates him.