For me, the main values of Isarnia is as a titan hero, but once costume bonuses have been gained, I think the OG could be at least as good as the toon.
Extra damage, with other heroes, has been 20-60%.
But it’s the def down that’s already of great value against titans and perhaps Toon Isarnia is mainly a rush event hero, and having already gained one Isarnia costume (all you need for the 5% mana), I’ll wait to see toon Kadilen before spending my keys. I use OG Isarnia against all titans and would only consider the toon against red.