If it helps any, I toooooootally feel your struggle. We have a big side yard and a smaller back yard. We never used the backyard before the pool. I was only ever back there to mow the lawn. Hanging out at the swing set or giant fire pit was all in the side yard. It took about 2 years to make the backyard look as nice as the pool. The minute that was done we turned around and looked at the back of the house. Saw the 35 year old rotting deck and sliding glass doors that we had rarely used before the pool. Ick. Kiss another $15k goodbye to have new sliders to a second story deck with a 6 ft staircase down to the pool. Add some more to spruce up the same in between area that you have. It. NEVER. Ends. Lol. Now we sit and eat at the kitchen table looking out the perfectly clear sliders and unobstructed view down the wide stairs. (I suggested that one to you last time. LOVE it.).
Also another thought about the stone finish. If you do decide to do the whole bottom area across the back, it will be hard to tie in at the side corners and you will forever be looking at them from either end of the pool. Once you do the sides of the house the front won’t match ....... and so on .... and so on.....
Looking again at the pic, under the deck is gonna be a doozy. White lattice would both match the deck and break up the dead zone, but you’d also be closing off that window there so it’s not ideal. When I was at my local nursery this year they had a bunch of lawn ornament kind of things made out of stained glass. They had all kinds of sunflowers, butterflies, etc in many different sizes. So they were basically pink flamingos but much much prettier. Maybe a couple of those closer to the deck posts would help draw the attention from the underside of the deck.
And hang big colorful flowerpots from the outside edge of the deck.
Or red white and blue bunting under the deck and nicer stone planters with fake flowers at the deck posts. Sorry my brain is working in spurts today.