The PhilPapers survey also shows only about 19 percent of philosophers are theists. So most moral realists reject the moral argument. Doesn’t the survey cut against the second half of this claim?

Correct, and both numbers belong together. Most realist philosophers are not theists, so the survey supports the first half of the claim (realism is respectable) and not the second (realism needs God). The moral argument’s defenders are making a claim that most of their fellow realists reject, and that should be said plainly. Their reply is that the secular realists have not solved the grounding problem, only declared moral facts brute. Whether brute moral facts are acceptable is the debate, and the survey does not settle it either way.