A: Yes, we checked with Andy, and he rules that, unfortunately, Mix It All Up is a situation which could trigger You Can’t Take This Guy From Me (if the person playing the Surprise had Keepers that were being mixed, and not just Creepers).
We would agree — it is a bit harsher than average for Fluxx, but there it is. Fluxx cards can vary from harmless or ineffectual to… taking someone’s whole hand. It does tend to even out, on the whole, we feel.
If you really hate the card, feel free to take it out of your deck. Totally your prerogative! Fluxx is supposed to be fun, so if this takes the fun out of it for you, then ditch it. We want you to have fun!