I suppose we all don't see many people using Stone Giant. In my opinion, that's because it's too difficult to properly utilize.
It seems to be a ranged skill, but in ranged encounters you need to waste one use of the skill just to prepare it.
But the main issue is its unreliable stun. This game's PvP is all about reliable stuns. But with this skill you need 4 (four!) uses to get a stun fired.
In scenarios where you rely on this stun, it may not proc (due to the target's immunity or just because you mistargeted it) -- and you need to build up 4 uses again.
It's too expensive in terms of resources and - what more precious - time. It also makes it much more difficult to land it in CC-vulnerability window.
On the other hand, in scenarios where you don't rely on the stun, it may proc and cause CC-immunity on the target when you don't want it.

We all know DKs have a magicka whip, some sort of a mixed whip, but don't have true stamina "whip". Also DKs have all parts of a dragon's body represented within their skills.
All except for the tail. So my suggestion is:

1. Make this skill to operate within melee range as a mighty strike with a dragon's tail.
2. As now it also has dual type of operation (melee-ranged), keep it function as a stone throw with ranged targets. It may look like you rip out a rock with the tail's tip and throw it.
Or like you stomp and a rock flies up (as it is now), and you send it forward with the tail's punch. I don't know. After all, there are details like animation duration and so on.
3. Move Stagger mechanic to the other morph. It would raise up the interest to the DK heals in PvE. It will also add some feeling (or, idk, experience) to the skill, as now you
throw a huge terrific piece of rock, full of magma, and it deals nothing to the target, the damage isn't even a joke. But it heals teammates, what even may be more confusing
in terms of immersion. And also it's not always easy to land, coz you need an enemy target for it. So you always need to be facing an enemy throwing it with rocks. I mean,
what a great set up for Stagger mechanic. And also it would ease the DK tanks lives, as they need to spend their stamina on blocking, but not on spamming skills.
4. To differentiate the skills melee and range functionality i suggest add its ranged version some feature. Don't know exactly which. It could be a stun, that would, imho, increase
popularity of DK archer builds in PvP. But it in some sort contradicts with what i said about stun reliability. It may then just slow the target with its mud. Although DKs have slow with the Ardent flame skills. Then it may not slow the target, but cause the enemy player to see dirt chunks on the monitor that would lower his vision (within reasonable limits).

Having a spammable in Earthen Heart would also open a free space for stam DKs in choosing a stun skill, as now they need the Earthen Heart stun to proc Minor Brutality.

As a DK lover, i really wanted to utilize this skill in PvP, but i just couldn't. And i still hope