You claimed that he killed SEVERAL of them, which he did not. He killed one and for all we know Diableri could just be incredibly charismatic and one of the weakest ones. So saying that Galactus defeated him doesn't necessarily put him above T n A.
What we do know is that Galactus was defeated by them, they have been claimed to be his equal several times, they are beings of "unimaginable power", they wrought more havoc than Galactus, ONLY the crunch energies could contain them and that he didn't kill them for some reason.
Now please, come back when you've read the comics.