Yeah, I was pretty much pure lightside, but still didn't get the lightside ending. (Both lightside and darkside seem kind of hard to get without knowing what exact choices you need to make to bring them on, so I suspect going forward, the "neutralish" ending will be canon.) I don't think that the ending really cares at all what you do with Jaedus. (Although maybe it does a bit in the darkside ending.) Which is weird. (Blah, I really wish they'd kept all five - it makes so much more sense.)