Everybody wishes they had a Scorchers bowler!
The Thunders biggest issue is that if Watson doesn't fire, they're in trouble. Sure, Buttler hasn't started well but the rest of the Thunder batsmen are unlikely to take the game away from the fielding side. They're there to support Watto.
Having had and lost players of the calibre of Kallis, Hussey, Russell and Khawaja for various reasons would leave a hole in any squad. It's hard to attract and replace top draw talent in the BBL due to player availability.
The Thunder has always seemed to rely on older players which leads to a constant need for replacements instead of upgrades.