I have a 30lb anchor on my 18 x 54. I am usually pretty loaded up with gear/people/dogs/beer and I can't get boat to stick in all but shallow slower current. I have not had this problem in other boats.
I currently have the anchor dropping straight off the pulley out of the transom. Does the anchor arm change the physics in a way that could improve anchoring, or does it just create an unnecessary obstacle?
Holding power relates to anchor scope. The higher the rope leaves the boat, the more line needs to be out to achieve the same scope. My anchor line exits about half way up the transom - if your anchor arm is mounted at the top of the transom, you'd need to let more line out to achieve the same holding power.