I don't think either of them can, unless a new character is released. To solo Sith raid, you really need to rely on ramping or otherwise through-the-roof damage. I did a calculation just for phase 2, and even if you had a perfect tm loop where Sion only gained tm through the 5% from damage (which will happen as he has no topple), then each time you do damage needs to be about 174k. That's with an absolutely perfect tm loop.
SLKR can do the whole raid because he gains unlimited Mastery from Siphon. JML is capped at +100%. SEE in theory can keep stacking it, but it relies on Linked and Deceived enemies taking turns...so you may need to keep adds alive to get it to stack, and even then I don't think you can do enough. Let's say you had Marauder to do huge hits--one way to get that up is to give yourself Revan's debuffs, but when he's not lead, he needs to do his AoE, so then you're potentially killing enemies that you need alive to stack your Mastery. Also I think enemies can't be Deceived anymore after you hit Ultimate.