Well, I've only used Shedinja once against Valarie, sure it helped me win the match, but it was hard to actually KO her mons at that version since they were mostly bulky and I only used offensive moves, so that's maybe why I don't appreciate it that much; seeing how you've described it, it does sound quite cool and I agree that it would be nice if it had better speed and might as well include better attack in, I suppose.