I guess I don't see that much of a difference. I'm not actually casting Umbral Soul when enemies are onscreen even when I do have it, so the difference feels pretty minor. What I AM disappointed by, though, is that there doesn't appear to be any way to pause your timer out of combat, which makes all dungeons past level 70 just a little bit more annoying because you have to periodically hit Transpose or Umbral Soul to not interrupt your Polyglot generation.