Did they change the tooltips on the spear? I don't recall there being any mention of it using your save DC previously - especially since not all classes even have a spell save DC in the first place.
Magic items that don't require attunement by a spellcaster almost always have fixed DCs, tied to the item itself rather than the user, and given that Larian are ducking out on attunement entirely, I'd expect that all effects that come from items and can be used by anyone regardless of class or casting ability should have their own fixed DCs.
That said, a DC of 8 IS far too low, regardless, especially since it's got such a specific niche. For weapon with an effect so incredibly specific, the DC should generally be a very hard one, since the item is tailor made for that single situation. For a spear that only works on eye tyrants - an already quite rare creature, comparatively, I'd expect a DC of at least 17.
