Yeah, Death of the New Gods is an enormous outlier for both Darkseid and the Source. Not just in terms of feats but characterization. The depiction of the Source is completely incompatible with any other comic, and even Grant officially retconned the whole "black/white humanoid Source" thing.
In this
scan you can see the official rejection of that whole aspect of the storyline. It basically retcons the "Source" in DOTNG as just being the humanoid form of the Anti-Life Equation, the Source itself is above Anti-Life and isn't "half of it." In Grant's work,
the Source is just another name for the Overvoid, which is why the map labels the white void outside creation as "Overvoid" and "The Source" and Darkseid doesn't come close to scaling to it.
Grant has said in an interview statement that Countdown and DotNG are apocryphal. He incorporated some elements of the story but only the parts that we actually see reflected in Final Crisis directly are considered canon.
In pretty much every other storyline, the Source is literally a God to the New Gods like Darkseid and is far far more powerful than them. In modern canon the Source is the supreme being above Perpetua and the Super Celestials, etc.