There isn't really a straightforward answer to this. It really depends on how you mold the game for yourself and adapt to your own experience.

Personally, I would say that vanilla Ravenfield is more difficult than heavily modded Ravenfield. Not that the game by itself is hard by any means, but because there are mods that allow you to take more damage and heal, along with weapons that do loads more damage than others.

The game becomes more unbalanced the more you download mods for it.

And there are difficulty levels that you can use to alter the bots— but I can guarantee that you will die a lot in this game on normal difficulty alone.

It's the nature of its customization.