You're assuming Caspius was going to lose his conflicts, and that he was a poor diplomat. To every man his opinions, but Caspius did manage to keep Sorraine in a good position whilst being alive.
You're assuming an awful lot about Aeneas as well. He does believe in war etc, but not for bloodlust and that seemed the apparent difference between Caspius and Aeneas. He's also seen the CoI fall before and is hellbend to ensure it doesn't happen again. The political atmosphere which was left to Aeneas is difficult and needs to be handled first before the CoS wishes to accomplish greatness again.
