A faster rod can in many cases reduces the number of false casts—especially when paired with a proper beach line--needed to send line a good distance. In my experience, false casts when beach casting are largely unnecessary and often cause problems. I don't want to carry a ton of line--just load and shoot. If you cut your casts down by 50-75% over the course of a few hours that’s a major benefit to anyone’s shoulders/fishing/hookup rate.The OP said that casting his current 6wt can make his shoulder ache yet most of the replies - except for the Ion XL - have been for fast-action rods that require more speed/power to cast effectively, where a softer rod should reduce the strain.
Is there something about Washington beaches I'm not understanding that make a fast-action rod cast differently than casting itinto a river or a lake?
(I agree that a session with a casting instructor might identify a problem. It worked for my achy shoulder.)