That dream was season 9 already for Dallas. After 8 very, very good seasons.
Dynasty just had 2 or 3 good seasons, before crap and camp took over already.
I am always amazed by how many Dallas fans love to post on Dynasty forums about their favorite show.
Dynasty had some half seasons that were a mess, namely the first half of season six and the second half of season seven. In the peak seasons of its ratings (3-5) it redefined itself as a show about one-liners and fashion and style and one-dimensional characters, one where storyline coherence was a low priority, despite some interesting arcs (like Adam's and Amanda's with Dex). Based on many interviews I have read, that was a semi-conscious choice because while S2 did propel the show ratings-wise, it already undermined the foundation the Shapiros had created. After S2, conversations like the ones Fallon had in S1 about the sexism and racism at the upper echelon of DC no longer had a place, nor did Steven's and Claudia's soul-searching and Krystle's struggle with loving a man she increasingly recognized as ruthless. And the Pollocs were used to writing for daytime soaps, where characters never really grow and learn from their mistakes--they just spin around in circles, and that is what happened to the show's characters as well: Adam was evil, then he regrets what he does and turns good, then he turns evil again. (Come to think of it, not unlike Sue Ellen's "hey, I'm sober, no I'm not. I hate JR--no, I love him again" and Bobby's "I hate Ewing oil and dirty tricks--I'm out--no wait, I'm in and I'm gonna out-JR JR."). And so on and so forth. If one has never watched either show and sits down to binge watch them now, Dallas
might be a better viewing experience as there are many seasons of a continuous thread. But at the time, even though Dynasty came second on the scene, it defined prime time soap on people's minds (which you allude to as well with its influence on other shows--even Dallas tried to stop looking so cheap). People can look at a trailer now and old episodes and proclaim "that's Dynasty" or " it's not." It became iconic. Dallas was too parochial stylistically to achieve that.