Telluria on wing is not good, even in her initial release to Beta I would not have ever recommended her there.
Mana delay so late in the match won’t make a difference, and anyone can patiently charge their skills while taking meager damage from her to pick her off.
Telluria’s damage is bad. It was never really meant to be the selling point of her skill anyways, but just to show how bad her damage is:
She hits all enemies for less damage than the weakest hit-all 4* hero, and just slightly harder than the strongest hit-all 3* hero.
But again, her damage has never been her selling point, even initial beta release. Her support to improve her teams longevity through mana delay + HoT and minion combo is her main selling point.