I'm not so sure that tere would be fewer boats on the Cowlitz than on most of the OP rivers in late winter. After the December mayhem things ususally quiet down a lot down there, especially when fishing is slow.
And the guides who stay still get into fish if they work at it. Most of them move up to the OP with everyone else and his dog.

I'd bet my favorite wiggle wart that you could count more boats on some of the Hoh, Bog, and Sol duc runs than on the Cowlitz after Jan. 15.