Could Spectre........

Melt these characters the way he did Darkseid (yeah I know he was reformed, but it still counts) and Star Sapphire during the Infinite Crisis?

Hulk
Supes
Black Adam
Thanos
Thor
Herc
Gladiator
Plastic Man
Swamp Thing
Lobo

Yes?

Depends on the Spectre, and how badly he's jobbing that day.

There's no reason why he couldn't outside of plot device, jobbing, or PIS.