Caedus, he is just that powerful.
Kyle Katarn wasn't even considered powerful enough to deal with Darth Caedus, only Luke himself was seen as his match.
And I would also like to add that I was very disappointed with the way they killed off Darth Caedus. I mean all that backstory and all that talk of destiny and then he just die like that...
When you spend however many hundred years of something, just instinctually holding back, you just cant deprogram yourself to just flip a switch and change it. I guarantee you, if yoda could fully tap into his force knowledge, and beat sidious, but that meant him delving a teeeeensy bit into quasi=darkside, he would have never done it.
Well I can tell you right now that all this speculation about Yoda not going 100 % is wrong. Why? Simple, in the Revenge of the Sith novel (not movie) one get to be inside Yoda's head while he fight Sidious, and when he realize that he can't beat him.