Do the limited points of similarity of ancient cosmogonies (and theological elements, such as the “divine council” and speaking things into existence) make that of the Hebrews less credible? Why or why not?

It seems not. No other cosmogony has significant enough similarities to be plausible as a sole or even main origin of the Hebrew cosmogony. All of these texts are hard to date precisely. Finally, we have independent theological reasons to find Genesis 1 plausible, and if God shared that story during some antediluvian or patriarchal ages (not with Moses himself, which is another possible original source), then we might well expect to find multiple pagan versions of the original story, i.e., versions of the Hebrew (Yahwist) narrative twisted by pagan cults, handed down from days gone by. In that case, the similarity with pagan accounts means only that the pagans misrepresented the truth, and that Genesis 1 is adequately reflects the original, faithful source.