Doesn't thrawn have better heroes, and thus can make entire fleets more powerful with combat bonuses as a result? Thus thrawn can be more efficient with his power at the cost of a permanent reduction in power if a hero is lost.
Palpatine can build and replace more powerful ships, but many are battlecruisers and SSDs that are more vulnerable to bombers.
Unless I've misheard the 2.2 playthroughs....
Thrawns not useless, add a fleet of smaller ships like carracks and strike cruisers and his fleets an put out some serious pain. Killed a SSD with a fleet like that 0 losses.