What dictates when these can drop? I've had a Vet 16 character who's maxed out in Enchantment and also skill points in enchanting skill line however only had 1 Kuta sent via hireling in 6 months and never farmed one even though i pick up everything i see. I've then started a new alt who's Vet 7 and spent 1 skill point in having the first level of hireling and nothing else and running a dungeon in Glenumbra which was Vet 1 I managed to get a Kuta Runstone. Is Kuta possible at any level regardless of location/skill points spent?

It's just a random chance. Which is very low. Best way to get Kutas are doing the writs.

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The Elder Scrolls Online

Kuta Drops