I'm going to assume you meant Grand Admiral Thrawn, but he had nothing to do with the Sun Crusher or the Maw installation it was built at. That was Admiral Daala, and the Maw installation was built by Grand Moff Tarkin.

Thrawn, meanwhile, was not a fan of super weapons. He didn't need them. In practice, they're impractical outside of generating fear, but they can't be everywhere.

Thrawn could probably defeat a Borg cube with a standard Imperial Star Destroyer, though. Although... the Borg lack anything you could consider "art", but they're not particularly creative in their tactics, relying more on their superior technology and adaptability to overcome adversaries, so i don't think he'd find them overly challenging from that perspective