It hits really hard for a support character, one of the few that can damage high health characters behind Zarriss.
You can use basic on stunned characters to shut them down for 2 turns, meaning you get to ignore them for awhile and focus on a new threat. It works on basically anyone the turn before their cooldown comes back buying you an extra turn before they can use a Special.
A fast Thrawn giving DT first turn for AoE cooldown increase, then him getting to ability block them the following, is a match made in heaven. It basically just takes any character that doesn't have a brutal basic out of the fight, since in my experience at least, matches are pretty much decided in the first couple rounds.
It also stuns, so serves a dual purpose against those with hard hitting basics.
Granted, it's not as good as GAC or Fracture, but it's a big part of an amazing kit. There's a reason Thrawn is pretty much universally considered a top 3 character, and the basic is a big part of that.