I think the religious angle isn't a general criticism as much as a counter to the specific narrative that the TESCREAL ideology is somehow rooted purely in logic and realistic evaluations of technology rather than in fantasy and wild speculation. The criticism of how it rhymes with certain elements of fundamentalist Christianity are usually rooted in this same observation, as well as in the fact that the elements of Christianity that TESCREALism most closely rhymes with are themselves harmful or insane regardless of what kind of wrapper you put them in. Like, both Christian and Singularitarian eschatologies use their faith in apocalyptic prophecies/predictions to devalue action to address very real suffering in the here-and-now in favor of trying to improve the lot of humanity in this hypothetical future, which just so happens to involve preaching more Christian/Singularitarian end times crap and also giving insiders to associated organizations lots of money and power. There's a leftist version of that too and it's also pretty fucked up.