But it's definitely wrong to equate Ford's fusions (wasn't that a make of car?) with the QuchHa'. Yes, they have one thing in common -- explaining the smooth foreheads via an infusion of human DNA -- but the important stuff, the history of how and why it happened and its meaning and impact within Klingon society, is all completely different. "Fusion" is a term that has a specific cultural, historic, and functional significance within Ford's Klingon society, and you can't divorce the label from that broader context and pretend it's only about the genetics.
Oh yes, I didn't mean to imply Enterprise somehow brought The Final Reflection into line with the rest of the Trek fiction produced in the last 30 years. I do think Enterprise may have partly been inspired by it with the human DNA thing, but as you said everything else is completely different.
That said, The Final Reflection is easily my one of my favorites, a true classic that I think holds up even now despite the inconsitencies with the direction TNG went regarding the Klingons. Whenever I read a reference to the book in a more modern Trek novel such as A Singular Destiny I always smile.