Interesting thought, Extol, which brings some focus to my reflection on the book. I think I agree, as Peake revels in Flay when he undertakes his duel with Swelter. When Flay's passion is aroused, he becomes much more interesting, but of course this puts him outside of Gormenghast acceptability.
I also think Prunesquallor was the most fascinating character. His outward 'humour' is an act - he's the most serious character, and the only one I think who sees the absurdities of castle life but he has found away to live with them. His thoughts are quite unlike his daft overly flowery speech.