Just use your Thorn for travelling as much as you can, especially in your 45 seconds of post mission wrap up. Of course walls are great to grapple to, but get comfortable pointing at the ground and finding that sweet spot that is far away but also still in range for your Thorn. To grind this, I did Code Level 2 Operation "CG2-3 Cloister: Reach Objective" over and over. I went into the first large room and eliminated the 4 flying enemies there. From there, I grappled around/in between the pieces of cover in a square-ish pattern. I did that for ~9 minutes then headed for the exit. (You can almost certainly fail these missions and still make progress towards this trophy, but I was paranoid and finished each time).
Keep grinding, stay persistent (I was questioning if it was working towards the end) and it will pop eventually (it pops mid-mission).