So far what I'm doing for 4th job Paladin since resets...

The TS does not use shields, so Guardian isn't much of a conversation here. I also highly doubt CO will raise other skills passed max as well, even in the future.

I too using 2H weapon, guardian does increase your defense against attribute and abnormal status attacks without needing a shield, equiped with a shield will add the blocking part. I did noticed sometime I were able to repel 1/1 at bosses, but not sure if its DS or anything else.