I have just posted a guide on my melee summoner and since he plays alot like a tanky char that does enough damage i would suggest doing some tweaks on the guardian skilltree that mimic that playstyle.
Imho key would be to make shield turn as spammable as dark offering is (maybe shield throw too as an option). That way the guard could play similar to the summoner with spamming a few standard attacks (shield bash or SOR) and get in shield turns more often for aoe clear. Dark offering sits at 3 seconds Cooldown and Shield turn at 8 seconds. Offering has a huge AOE and shield turn does also need the taunt to make gamplay not clunky.
Therefore imho the guard alos needs a tweak on the point investment.
I figure a shield turn build could to look like that (10 points overhead with +1 +1):
Shield Master needs probably to be tweaked too. It is probably a tad too low.