I guess we have been lucky. We have stayed at SSR several times as well, and have not waited more than the posted 20 minutes ever. Most times, we have waited less than 10! Of course, YMMV, and not every person has the same experience!
I know that some here rag on the buses because it takes away time from the parks, but we don't look at it like that at all. We view the buses as time to relax and meet other travelers. For us, they are part of the vacation. Of course, since becoming DVC members several years ago, we never commando the parks, and spend a LOT more time at the resort. For us, the quiet pool in the Treehouses was that - quiet! We would have liked a pool bar, and there is space for one, so hopefully Disney will open one, at least during the day, at some point in the future. It is true that if you want to go to the main pool, it will be a bit of a bus ride (usually less than 10 minutes when we used it), so while a bit inconvenient, it wasn't a deal breaker for us. If your Treehouse ends up near the Grandstand side, the walk to that quiet pool is only a few minutes, and it does have a pool bar open during the day, along with a play area for younger kids!