I thought we'd agreed the type shouldn't have (stone giant) in it, on the basis that a regular wight doesn't have (human) or the like as a tag and isn't affected by human bane weapons. It's just an undead.
The same should apply to an undead derived from a Stone Giant, especially as the living giant doesn't have Huge giant (stone giant) as its type.
The Stone Camouflage just uses "cairn" in the Cairn Wight (Undead Stone Giant) since it's a "racial trait" possessed by all cairns due to their stone giant nature.
Although come to think of it, shouldn't that apply to Sunlight Sensitivity too?
The Rock Bowling has an obsolete wording. The Enworld version uses "The cairn wight send a rock tumbling along the ground in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 19 Dexterity saving throw, taking 28 (4d10 + 6) bludgeoning damage and falling prone on a failed save, on a success they take no damage and remain standing."
Oh, and I tweaked the Description so it has "These stone giant wights possess the intellect of their former selves" instead of "These giant wights possess the intellect of their former selves" so we have at least one use of stone giant wight in the text.
Come to think of it further, I decided that wasn't an issue since there are some cairn that aren't sensitive to sunlight, such as the Cairn Zombie, so the wight should have "cairn wight" in that trait.
Also, I wouldn't have it do 2 levels of exhaustion per hit AND give it two attacks with Multiattack. With its Legendary Action option the Wraith can make three exhaustion-inflicting attacks per round so can kill a PC in a round if they're unlucky.
Contrariwise, at most the Cairn Wight (Undead Stone Giant) can only do four levels of exhaustion per round, two with its standard Action and two as a Legendary Action, and the target has to fail two DC 10 Constitution saves for that to happen (since it must miss its DC 15 CON save by 5 or more).
Now that I think of it, that DC seems extraordinarily low for a Challenge 16 creature. The recommended DC for a CR 16 creature is 18 after all.
While I did deliberately gimp the DC by making it CHA-based instead of CON-based like a standard Wight, maybe we should go back to the default and make it CON-based for the Cairn Wight, which'd give its Death Grip and Soul Drain DC 19 (so the target would have to miss a DC 14 to get two levels of exhaustion, which is pretty easy for a Challenge-appropriate PC).
Oh, and the Cairn Wraith's "Life Drain" should use base 8 for its saves, not base 10, which'd make the DC 16 rather than 18.
The easy fix is to increase the CON a bit and knock off a few HD.
Both Wraiths and Wights have CON 16 (+3) in 5E so I think you'd be justified in giving a Cairn Wraith the same CON 22 (+6) as the Cairn Wight, or if you prefer to keep the DC 18 make it CON 20 (+5) like a living Stone Giant.
I lean towards CON 20 so the Cairn Wraith is a bit more ephemeral than the Cairn Wight.
Either way you'd need to knock off a few Hit Dice assuming we're aiming for the HP to be in the same ballpark of 209.