My Babylock only has the thread cutter,but i haven't used it that long.I have had my Pfaff over 20 years and I'm still using the same needle threader.You might check that little hook that goes in the needle,it might be bent.
If your thread cutter cuts slow i would think it would cut the thread fast.But maybe it's missing the mark inside going fast.To bad you can't see inside when you are pushing the button.Just one more thing to go wrong with these machines.Connie in CO