I used to deadlift and can't say they did anything for my traps. The best trap recruitment I get (may vary, this is just ME) is from: farmers walks, kettlebell swings, any type of powerclean movement (which is why KB swings work). I'm on the fence with shrugs but not done them enough.
My traps look minimal square on, but pretty awesome from the side. Attachments and all that vary.
Btw only when I started farmers did my squat bar position improve (through growth of traps).
Good progress. Keep it up
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