They definitely will not be "irrelevant." Lots of people fall into the trap of thinking that any squad that can't take #1 in arena is "useless," and that's the stuff that GAC losses are made of.
Go for Jedi Revan first. He's easier to get and build a squad around, and is much more versatile. He can crush it in raids or PVP, whereas Darth Revan is pretty much tailor made for PVP.
Also, as was already pointed out, you'll need Jedi Revan to get Malak, and Darth Revan really needs Malak to realize his full potential anyway.