Agreed on the Halberd. +1 boosts him to S5,and he can try for Iron Arm when rolling powers if he doesn't think that's enough. His basic Nemesis Force Sword is great for fighting Deathwatch (Knighty: Think Power Sword with Force special rule).
He likely grabbed the Hammer and didn't realize he was replacing it, rather than adding to it ("may take items from the Melee list" sounds like it, until you actually read the text above the Melee list).
Unfortunately, calling mistakes like this one requires a lot of knowledge of your enemy's codex and even then you'd rather have the Codex on hand...
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.