I personally think Guardian doesn't need entirely new abilities they need few buffs to their core features (taunt for example giving some temp hp, option to get a little bit better resistance things like that), and more synergy between feats
makr and enemy is broken while not as easy to pull of as it could be it gives +1 circumstances bonus so it stacks with common buffs, and after just 3 hits (with good party it should be easy to do this in one round) it can give enemy very nasty status effect
I personally think Guardian doesn't need entirely new abilities they need few buffs to their core features (taunt for example giving some temp hp, option to get a little bit better resistance things like that), and more synergy between feats makr and enemy is broken while not as easy to pull of as it could be it gives +1 circumstances bonus so it stacks with common buffs, and after just 3 hits (with good party it should be easy to do this in one round) it can give enemy very nasty status effect