I'm here. I've been absent this week because I went up-north to cabins/cottages that had neither cell nor WiFi coverage. That takes a few days to get used to, but there's something to be said for disconnecting now and then...
I'm surprised that your humidity went that high. I have Nest Thermostats in rooms on each side of the pool room. The bedroom always reads slightly higher, even though I keep the door between the bedroom and pool room closed. I attribute that to the fact that the bedroom has lower ceilings and gets less light and air movement.
The Nests have a "cool to dry" feature that will run the AC if humidity reaches 65%. It hasn't gone that high. If it were adjustable, I'd set it to 60%.
It's unusually high right now (61% and 60%) because of the weather we've had this week. The Nest history report shows that the AC's have only run 1 hour since last Wednesday. Typical summer humidity levels for my house are in the 50's.
The HVAC vents for the pool room are in the center of each window sill (above the candle fixtures). I keep them closed when the pool is cold because the pool room doesn't seem more humid than any other part of the house... Evap is quite low. During swimming season, I often just keep the fill hose connected at the side of the pool, but right now I have it stashed away in the closet because I don't have to add water very often. Another difference could be the shape of our pools. My pool is smaller, but also deep, so mine has much less surface area than yours.
I never pursued quotes for epoxy. It was hard enough to get the resurfacing quote. During the demo the contractor showed me a sample and explained the "layers" of my failing surface. On top of the gunite was: very old plaster, then perhaps paint, a layer of fiberglass (I later found "Fibertech" receipts), and on top of that some type of paint or epoxy. I haven't heard many happy stories of paint / epoxy, but I have to say that whatever the top layer of my pool was, it was holding up well. The failures were deeper. Thick chunks of the surface were breaking away. I had everything chipped-out down to the gunite. The total cost was $8k. I had upgraded the plaster, and the contractor blamed what I thought was a high quote on dust containment, access issues etc. In reality, I think supply/demand had more to do with it. Most places I reached out to didn't even respond. Some said, no/not now, others stood me up. Two showed up, only one of which provided a quote. In the middle of the job I realized that his crew did the demo, but he subbed-out the resurfacing. (live and learn - it didn't occur to me to ask about that)