Other Weapons

If hypothetically these enchants were found on other weapons, would those weapons gain pierce effect as well? (Assuming they don't already have pierce.)

Technically speaking, yes. If they were on non weapons, your character would gain a default piercing level.

But there aren't any non-lance-only piercing enchants...

Penetrating Gathering Knife from gachas

That sounds amazing.

Stiff penetrating gathering knife - Diggin' deep into the sheep for wool. Anyways, it doesn't explicitly state any piercing increase (Like, the blue text for weapons with the default piercing levels).

Why isn't it on the enchant page though?

Because people tend to only put the item in the event/gach page, and never the rest of the pages.