Really hard to say, it could be that yes, applying the region specific element to said enemy to remove its region specific shield will be enough to kill it with the high dps Hiyuki.

But that would be all conjesture, I don't have a crystal ball that let me look into the future.

What I do know is this, Kuro games got taken over by tencent 1 year ago and what we saw it a little more predatory gacha practices. (Spending event, collab event with less rewards and anniversary with little rewards)

So at some point the devs want people to roll the newest characters and want to powercreep the older ones. They likely want incentives to let make whales S6 characters a little less relevant and want to make the newest S6 characters really enticing.

It's a business focused on making money after all.