Thanks for looking into it in more detail.
I think I’d prefer that we focus on the collectLabels function first as I just mentioned in Experiencing severe Kee related slowdown on website
Although this is not shown up in your profile, I’m not sure whether that could be due to a limitation of the profiler and it is one of the few bits of code around this part of the extension that has changed recently so it may well be the cause of your problems too. If changing that function doesn’t help, we can consider introducing additional handicaps at other stages of the getFormFields loop as you suggest.