I absolutely agree about the KOTOR story and the antagonists in it not necessarily being big enough to warrant an anniversary release. I was just using that as an example though, along with the two recent movies.
I also agree that Sith are already pretty solid, but just because they are solid doesn't mean more can't be added. A character doesn't have to be game or meta changing, nor does it have to be 100% unique. I mean look at the jedi characters we have in game, 3-4 of them have extremely similar kits and most jedi kits are fairly underwhelming in general. Also, just because one faction happens to already be really strong doesn't mean that it should be ignored when releasing new characters. Jedi could easily be buffed to be on par to sith if the developers went back and reworked some of the existing jedi characters, like they did with grandmaster Yoda. Reworking older characters and other content is part of running a game, especially when new characters are released in limited numbers and aren't easily obtainable.
Additionally, I think that one of the biggest issues with this game is that most new characters have to have some kind of wow factor and be game/meta changing in order to get people to spend money. And that's fine and all, but it's not the only way to draw people in or get them to spend money. Everyone wants strong characters, but alot of people also want characters for the sake of nostalgia and some people just like to collect characters. They could easily make some decent characters that are viable for different faction/team synergy that are not overwhelmingly game/meta changing, but that are fan favorites and still make a profit. There are plenty of star wars characters that could be released that have this nostalgia factor, both from canon and extended universe (both are fair game since KOTOR characters are already in game and are from the Legenda/Extended Universe). I just think that with all that they have to work with, that we'd have a little more of a balance between dark and light side characters at this point.