I run the same with both EP zetas and the zeta on Vader's unique. I lose to faster Vader's, as does just about everyone running that comp. DT/DK are a great pair and work well together, but neither are an easy farm. There are a few shores on the shard, but honestly the tank doesn't help all that much - it just gets fractured, then if the opponent is running Thrawn and fractures your Thrawn (which is likely because of the size of his health + prot pool) then it's a very easy match. I'm gearing a four star Sion to be able to plug-in, but am not close to Nihilus, which is where the real synergy lives. Thinking next zeta is probably Tarkin's unique over ebb and flow because he's essentially functioning as a tank and the TM Removal / Offense Down benefits are pretty substantial against all comps (and I'm a late September start, so there aren't any Chimaeras yet - the zeta keeps you faster than everyone else if it comes down to TIE Swarm).