Responses
I think it does make sense given the context of the story, since Oshi no Ko is built on lies. Ai lied not because she wanted to hurt others – Ai wanted to reciprocate the love she receives, but she can't due to her trauma, so she tells lies like wishes – that they'll turn into truths someday.
I can't sit here and pretend I know Kamiki – I'm too brain dead to read back and make speculations, but the line is just Aqua pointing out the glaring difference between Ai and Kamiki – their intentions and how that shaped their lies and their consequences.
Can correct me if I'm wrong, though.
"You are a nasty liar who has been telling lies for your own sake"...
What's next? A sinner committing sins?