1st: GSSBlunaspike is correct, a build you use in PvE is going to differ than PVP and in doing map completion as a guardian almost any build works except for when you are trying to solo champions.
2nd: Taking a look at your gear/stats unless you transmogged everything it doesnt look like your in full exotics, therefore if you are going to PvP that should be your first investment, I promise it will help.
3rd: “I’d like him to be a PvPer, one that can go toe to toe with anyone and still be a benefit to his team.” I don’t know exactly what you mean by standing toe to toe to be defined as killing or not dieing in a 1 on 1 so clarification might be helpful.
4th: Assuming PvP means WvW build (different than sPvP) you have to also look at the people you are going to run with, a zerg build and a small group or a solo roamer build is different.
Clarifying all of those will help us greatly in assisting you in being a bad-kitten guarding.
P.S. Guardian is a front-line brawler that can heal, yes ELE can out-heal us in groups, and yes warrior can out-brawl us but we do both well enough. Just in response to GSSBlunaspike’s last sentence.
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