I did it. I finally threw out my Thai con.
I got it as a cutting via Facebook marketplace and picked it up in a parking lot for very cheap right before the prices for these dropped, so I've been very precious about it. It never looked especially healthy; I'm pretty sure it has been the source of my thrips for a couple years. I tried everything, but they always came back, and they were always the worst on the Thai con. I have now thrown out all of my houseplants except for a single tiny succulent (sentimental).
It was hard, but it was not fun any more, and now I am starting fresh.
Thanks, that's all