The last barrel I shot out went to the gunsmith first. He looked at it and said "looks like the throat is going, but it is also loaded with copper. Let's clean it and see what happens." Cleaned it and still shot like crap, so we rebarreled it. Not sure why someone would be averse to 15 minutes of cleaning first.
Wouldn't hurt to try, but I'm with JB. Two thousand .300 Wby. rounds is probably the life of a barrel. Even if cleaning helps, my take is like his, more than likely needs a new tube.
I hadn't thought about sending it back to Wby, but I would bet the price for a new factory barrel would be a lot less than a custom job by a smith. And Wby. barrels are pretty good.
And with his "mother load" of brass, no way can the OP justify changing to another round...
DF