I haven't checked, but I bet you use about the same proportion of both event and item cards in any given game relative to the deck size, but the raw number of items you use is much fewer.
Not even close.
Barring special haunt rules, it's always possible to obtain every omen in a given game (if you explore the whole house), and it's typical to draw roughly half of them before the haunt even begins.
Items are actually a larger deck (22 vs. 13) and you typically get fewer of them. Around 10-30% of the deck is pretty typical in my experience. Fully exploring the house (including the vault) only gets you 6, plus probably around 2 from events along the way.
So, yeah, it's completely normal to use most of the omen deck and only a small part of the item deck in a given game.