Jaws is one of my favourites, too. A zombie and a shark are scary to be chased by, but are innocent themselves, really. The premise of shark/zombie films tends to be innocent people defending themselves from a predator that has no control over their impulses. So that's grand, even when it gets bloody and violent.
We will have to disagree that the graphic scenes take place off screen and things are left to the imagination... I wonder if you are possibly comparing it to even more graphic on screen depictions of torture if you have seen lots and lots of this type of scene.
Granted, like @LittleJustice, when it began I had my eyes screwed shut and fingers in my ears! Seeing the aftermath was the worst part for me.
Almost all reviews on Rotten Tomatoes agree that this director used graphic on screen depictions, whereas previous directors did much more of what you're suggesting, and let the audience use their imagination to fill in the blanks. I don't think the first few films even had the budget for anything more than that, anyway.
But ultimately my issue was not with the graphic gore itself, but with the cruelty.
I'm also not sure that Billy Crystal turned to religion. He was already religiously indoctrinated as his father was a pastor, and he was a small boy when he saw his father zombified and killed. Childrens minds forge their own narratives to survive, psychologically, and the facts of the matter would never have been explained to him by anyone. His mind just merged his religious upbringing with his trauma, I doubt he had any control over it.
The other Jimmy's were also very young and may have had no one to confidently explain what was happening, because nobody really knew. They would have been terrified themselves. Religious ideology ie 'believe in this and our God/Old Nick will spare you and favour you' would have been extremely comforting and appealing to a child. They were all just terrified children.
Again, with Dr Kelson, he was obviously already a Dr so didn't turn to anything different in the midst of chaos. He was much older than the Jimmy's, so less vulnerable and impressionable, and just understood things much better having lived most of his life before the virus.
It's more about psychology and trauma than religion/Vs science, IMO.