Ascians are tempered. Tempered people aren't reasonable. Even Ramuh, one of the most reasonable of Primals, still has unreasonable tempered Sylphs. It kind of has to be that way. The alternative is "everyone dies". You could argue about killing him when we did, but how long can you keep him around without removing him as a reasonable threat? If the Ascians as a whole just took a step back and we focused solely on beating the evil empire I suppose it could work, but I don't really see that happening. They seem determined to finish things now.