I'm writing an essay for an English subject about the film The Shawshank Redemption.
I've used the sentence
But though the Warden presides over many prisoners, he is morally no sounder and stands less chance of reform.
My teacher has corrected no sounder to no more sound, but Microsoft Word identifies the latter phrase as grammatically faulty. No more sound does sound odd when isolated, but I can't put my finger on why specifically.
There are mixed opinions online, to the point that citing them here would do little good.
What are your thoughts?