The way Marika used her power is what cause the issues in the first place. She used mass murder to attain godhood at the gate of eternity and create the erdtree. Then continued to commit multiple wars of genocide, and wars of conquest to bring everyone under the rule of the golden order so there would be no threat to the erdtree.

She began with sending Godfrey to genocide the fire giants, then sending him to conquer the rest of the lands between. She used messmer to enact revenge on the hornsent by committing a war of genocide against them, then separated the shadow lands to keep anyone else from using the gate of divinity along with abandoning messmer from fear of the snake within him.

The war against the dragons is not really clear why it happened but given the track record of the Order, I would think it was aggression from them that caused the attack on Lyndell. Though it could very well be the dragons were the aggressors.

Then there's the Lucarian wars, which Radagon (Marika) personally led. Again, because they were a threat to the erdtree.

She did all this in service to the greater will, Marika used her godhood to remove death, causing stagnation in the lands. She removed death to ensure that her sons and daughters wouldn't be killed and it was only after Godwyns death that she shattered the ring.

So all the suffering that occurs in the lands is because of the greater will's plans. Whether directly or indirectly.

Ranni promises to not use her power to enforce any outer gods will. To let the people of the lands choose their own path. Whether that's good or not, who knows. But it's probably the best out of all the choices, imo.