>>38408000Realistically: I think Snorlax eats anything it can and doesn't make much distinction. I think it eats literally anything that isn't "alive" or can otherwise get away and will basically engorge and forage on anything from stripping entire trees, to methodically snacking on nuts or fruit, to just slogging through a corpse or carrion.
There's probably a lot of dead Snorlax with their stomachs full of plastic and garbage bags.
You do, though, raise a compelling point about Slaking, but I'm going with the 'Dex description in the sense that it's behavior of "laying around and eating grass before moving on" sounds like the kind of herbivore behavior of the Gorilla. That's what Gorillas do, y'know? They sit down and they eat shoots, saplings, leaves, fruit, etc.. While they "sit around", giving the impression of perhaps a lazy animal.
I'm going to extrapolate a little, but I actually think the deal with Slaking is it's secondary stage: Vigoroth, is an omnivore, and that it uses it's boundless energy, long claws, sharp teeth, and aggressive behavior, to both forage for food and hunt down prey. Vigoroth most likely do this to bulk up- roaming around in baboon like packs, before one of their alphas finally reach a certain level of maturity, body fat, and muscle mass, so they may evolve into a Slaking and go off on their own.
Slaking, then, restrict their diet entirely to fruit, nuts, and vegetation. It still has the guts of an omnivore though, so like a Panda bear it becomes somewhat 'sluggish' or 'lazy' and makes up for it's lack of a proper diet by grazing on a large quantity of vegetation and empty calories, while conserving energy through it's sluggish behavior.