Expiring contacts aren't as valuable anymore. So no, I don't think keeping dead weight on the roster instead of a valuable player in order to deal for a replacement for someone that got hurt after the deadline would have been better. You can argue that a different acquisition would have been better, though. Also, I'm not buying Thompson being the better defender at all.
I still think they could have gotten some big man who was more valuable than JO down the stretch, but your point on Expirings in general is valid.
As for Thompson, I'm only going by what I heard the Warriors feel nowadays. I can't say I've seen enough to make that assertion.
My basic point is that now that the season is over for them, Jackson has been fired...etc, I've heard that if they could have last offseason over, they'd have kept Jack and Landry, and not did the sign and trade for Iggy...They won't admit it publicly, but I've been told different.