I think the Christ metaphor is a relatively valid one. Let's not forget that Forrest Gump was often compared to Being There, and that's a movie that ends with a shot of the simpleton protagonist literally walking on water. It's a Jesus metaphor not for Forrest's own motivations or awareness, but for the hopes people project onto him (mostly during the "running across America" stuff) and for the incidental healing he brings along with him. Look, Jesus stuff shows up errverywhere in Western media because a) it's an almost universal touchstone and b) it's easy. It's not the be-all and end-all of Gump the way Bob seems to think, but it's there.
Where Bob's insufferable cuntery comes in is how he expresses this: implying he's got some special insight for perceiving incredibly obvious symbolism (don't you ghouls know about your fake-Savior and the fish? *sneer*), and in thinking all of this makes the movie shit. Just look at how condescending he's being about it (yes, condescending is Bob's mother tongue, but he's being especially bad here). It's very, very obvious he loathes this movie, partly because he hates any Christological imagery that's meant unironically, but mostly because it's a movie about a well meaning, very simple man from the South succeeding beyond your wildest dreams precisely because he is simple and well meaning. Just imagine how Bob must recoil from such a message, when he thinks success must be predicated on being an obnoxious, snide, Ivory Tower, coastal elite asshole.