So sorry you've had a bad experience. I've always torn off the papers before washing.
When I first started quilting through paper I used tissue paper. I found out the hard way that not all tissue paper is created equally and some had a thin coating of plastic or something and it was not good to use for quilting. Couldn't necessarily tell by price either but I could by feel so preferred sheets I could touch.
Have you tried a hard tooth or nail brush? I know we get to a point where we are simply done with a project, but it might not be too bad to do half an hour (one situation comedy!) at a time while watching tv. But yeah, it's going to be grueling and create quite a bit of fluff.
It's ok to give the chore to someone else to reap the rewards of your quilting. Do you have any sort of guild or local community to see if someone might be willing to do it just to have something to do. You never know, I accepted a UFO from a board member that I'll be sending back to her because I'm having a hard time getting started on my own projects but seem to be able to react to finishing things just fine. One of my small group ladies was having a similar issue (and we weren't meeting) during the early days of lock down and put out a request for unfinished crib sized projects, so I gave her the preemie tops and a couple others I hadn't quilted yet. Donations done, hands busy, win/win for all
