If you have an earth shift card, then Shift I will change earth cards to water cards. Which is nice because your earth shift card will then do critical damage instead of regular damage to those shifted cards.
However with Shift II , the way it works now, earth cards will shift to fire cards. Your shift card's damage won't improve at all, it will keep doing regular damage... Of course you could still make a deck to benefit from the shift with other element cards, but the complexity is a bit over the top for that and I'm guessing most people won't bother.
The mild change I'm suggesting for Shift II is that for an earth shift card, instead of shifting earth cards to fire cards, will shift death cards to water cards. So the shift happens "around" the earth shift card. (Death -> Earth -> Water)
This alteration actually gives an improved benefit over the regular shift, because now the card will deal critical damage to cards it used to do reduced damage to. And this type of shift is easier to use in a deck without complex setups with a lot of various elements.
I don't think it's overpowered either compared to strong healing, damage over time and rewind cards. It will be a proper support card.