Did some digging around the JP wiki.

There should be a change coming up to make her rampage skill party-wide by default. The difference between using a relic or not is the multiplier of the rampage.

Without relic, the effect of rampage seems to be 1.2 times while with relic it is 2 times.

So the relic is fine, it is just a different multiplier between using a relic or not when that change happens.

Edit: I noticed this on a couple abilities, mainly party-wide buffs that they are added seperatly instead of all at once. Not all do that, but some. Hell knows for what reason though.