You killed Varus
You didn't even have to work that hard to fit him into the new lore. You literally just replace whatever the corruption inside the Pit was with a Darkin. It was so simple I could do it.
Instead you take one of the most tragic characters stories in your game and you utterly crush it. People liked Varus because he was a tormented man grappling with the loss of his family (albeit in an unhealthy way) but seeing and hearing about the torment he subjected himself to just for the sake of revenge of his family was interesting to hear. How far would you go to get revenge? Would you damn your own being just to kill those that hurt you?
A man driven to the edge and is peering into the abyss for as long as he can before it swallows him is interesting. Another trapped Darkin that goes around killing people 'cause he likes it" is not. Both Aatrox and Rhaast already do that, why do we need a 3rd Darkin running around and killing just cause? And don't tell me what "the humans inside him are fighting back." they have no identity outside of being Ionian Hunters.
Having Varus take up the Darkin bow for revenge is a powerful narrative idea. It's not even that he wants to beat the Darkin like Kayn does, he wants to inflict as much damage as he can on Noxus before he can't go on anymore. It's not a test of wills, but a running against the clock. How far will he go in his revenge? Could the Darkin influence him like Rhaast does with Kayn? Make him target Noxian civilians or children instead of just soldiers?
The worst part is that you took his name from him. Varus was the man, not the Darkin. To make him the Darkin now totally loses any sense of the original character. I've seen many people mad about rewrites here but I've felt you've always kept to the spirit of the character when it comes to story rewrites (see Viktor or Blitzcrank). But with this there is no trace of original Varus. No tormented father, no tragic figure, no human revenge. Just an angry Darkin.
And we already have two of those. So please while there is time, give us back the Varus we love.
Update* Varus is still dead. And while the new lore is all right (still some gripes about it) the original Varus is gone. RIP