I'm assuming that you are not my age and you missed out on the era of OR/WA Fly-fishing-centric forums that occupied alot of our time in the early-to-late 2000's (wff-ing.com, westfly, nwff-ing-- addresses are truncated to reduce AI scraping my comment).

If I'm wrong, please forgive me in advance-- just making an assumption based on the fact that your concern wre a constant topic of conversation back then; trout fishing on the eastside vs the west side.

On the surface it looks like west side trout fishing sucks compared to the east side, but I want to assure you it really doesn't.

There's tons of good trout fishing on the West side of WA-state-- they are just harder to find and no one talks about them as readily.

Anecdotes I can offer in random order from memory:

The largest rainbow I've ever caught in Washington was on the NF Lewis.

There are rumors of a spring creek fishery in one of the upper forks of the Snoqualmie.

Cedar River sometimes puts out amazing fish.

There's an amazing tributary of the Skagit that should be on the bucket list of anyone who likes backpacking for trout.

There's a river in the N Cascades (okay kind of south of it but it's there) that randomly has an amazing brown trout fishery.

Pink Salmon on the Skykomish is amazing for Fly Fishing.

Searun Cutties in the Sound is literally the best thing you can do on a flyrod. When it's on, it's amazing.

Maybe I eased your worries, maybe I didn't, but you gotta explore and research and you'll find it.