Well, not sure what to make of this, but evidently my iPad was exhibiting this behavior because it was connected to power. The moment I disconnected, the lag/stuttering cleared up. Funny that a restart didn’t fix it, but switching to running on battery seems to have done so. My guess is maybe while connected to power it was trying to do a post-upgrade iCloud backup and it was stuck in a loop or something and when I disconnected it stopped it from attempting the backup. (I’m on vacation and the WiFi here is relatively slow, so that may be a factor for a poor iCloud backup attempt.)
Anyway, so far so good.?