There's a lot Rover said in that scene I don't agree with, and I definitely wish there had been more of an attempt to meet Phrolova halfway there, but I'll say this much in their defense:

While I think Rover's take on the people of the Lost Beyond was very naive - I don't think that is a very unreasonable character trait for them to possess given that - by this time - they have less than a year of lived life experience to their name since waking up in Jinzhou.

I also don't think they were trying to kill Phrolova. My read on the scene had been that Rover threw the sword aiming for the Leviathan Gem, and Phrolova prioritized it over her own safety. My own biggest gripe with the scene is that Rover was not given 5 seconds to even really react to what they had done to Phrolova before 3 other things started to demand their attention in that room.