So you're telling me that if Trigon was a fun demon who fancied possessing someone instead of enslaving the entire world then we could've gotten Dick to have a line and delivery that was as iconic as this:
I mean listen. I know being possessed by Trigon would probably straight-up kill you because he's insanely powerful and isn't your typical demon, but there are other demons out there bro. Ones that come from hell and that you'd need an exorcism to get rid of (enter Jason Blood).
The closest thing we got to Dick being possessed by some unhinged demon was Raven!Dick, and it wasn't even a possession. It was Dick battling against Raven!Dick to save his soul.
TNTT (Vol. 2) #3-4
Like dammit, give me a demon who possesses Dick and then goes to taunt Bruce about it.
Possessed!Dick: "I know you and Dick were partners for a long time, Bruce. It's too bad that you couldn't protect him after he strayed from your side. Maybe if you hadn't let him go so easily you'd still have someone to call your son. Oh, wait, that's right. You never did adopt him like he wanted you to. That really hurts him, you know. Not that he would ever tell you because he fears your rejection.
That's a shame, Bruce, it really is. But don't feel too bad about it. Dick has me now, and I won't abandon him like he always feared you would. I'll take good care of him long after you're gone."