Importance does not equal quality. The quality and value of the Hobgoblin stories is independent of the very little influence he ultimately had. People who write monthly comics and ongoing are often not the very best judges on to which elements are ultimately going to prove important and lasting. Readers and writers might well have thought that Hobgoblin was the big new thing at the time but that it did not prove to be is no fault of their own. To take an example from the movies. I personally do think The Dark Knight is a better movie than Iron Man 1. Both movies came out in the same year or in a year's difference between each. But ultimately The Dark Knight had far less of an impact and influence than Iron Man did.
Venom and Carnage were the biggest additions since Lee-Ditko. Achievement and impact is greater there.He was the first successful addition to Spider-man's rogue gallery in years.
Ulrich later became Goblin Knight, and IIRC, he's currently dead, but neither he nor Macendale were ever big villains on the scale of the original Hobgoblin and overall the stories of the Hobgoblin declined in quality once Stern stepped down. When people talk about the great Hobgoblin stories they are mainly thinking of the original arc in the Stern run and nothing else. Even Stern's Hobgoblin Lives isn't considered as great a story as his original arc. It's a big salvage operation.They could have easily capped him off with the Ned Leeds reveal and that would have been it. But they immediately replaced him with Macendale and then Phil Urich. So the identity certainly has legs.
Which again shows how intangible the idea of importance ends up being. For readers of a certain age and bracket, the Hobgoblin feels like he should be important. But if you step out and look at the big picture, he's not.I will agree that Norman's return made all goblins irrelevant once he was back. But nobody anticipated him coming back when Stern created him.
Let's say there's a One More Pumpkin Bomb story which erases all Goblins except Norman from continuity. More or less the long term serial arc and stories of practically all the characters except Harry Osborn, would be the same. There would be little long-term difference if Roderick Kingsley was erased from continuity or not. Because he didn't make any real impact on Peter and his major supporting cast. There's Ned and Betty but he could have simply died at the hands of the Rose or in Berlin or whatever. It wouldn't change anything.
That was already done by Conway when Harry Osborn became Green Goblin and Peter became alienated and certainly estranged from his closest friend. So the shadow and legacy of Osborn was already big and great without Hobgoblin in the picture. And Harry Osborn unlike Roderick Kingsley was directly tied to Peter and Gwen.The presence of the Hobgoblin doesn't take away from Norman. If anything, it adds to his legacy. Because, even though he had been dead for years, his shadow still loomed over Peter's life. In many ways, you could argue that Norman is indirectly responsible for the Hobgoblin's actions as it was his gear and journals that Kingsley used. Without them, there would have been no Hobgoblin.
What makes Kingsley interesting also weakens him as a successor to Osbor, is that he has no connection whatsoever with Peter Parker. I mean the killing of Ned Leeds isn't because of Peter's actions or choices or being connected to him. Him attacking Ned has nothing to do with Peter, since Ned was a Bugle reporter who got taken out in the line of duty. It's more or less like how Frederick Foswell got taken down by the Kingpin's goons in Lee-Romita's run.
The main value of Stern's original Hobgoblin saga is the extensive world-building that Stern did. He really did set up and show how smart and dangerous and resourceful Norman was. Basically an evil Bruce Wayne with multiple Goblin-caves across the city, with his own mobile (which strangely resembles the Ghostbusters car) and so on. Telling the story from the perspective of the villainous Hobgoblin who monologues extensively in thought balloons and word balloons is also interesting and in that regard it's a true ancestor to Kindred since that's how Spencer's Kindred talks and moves in his run. So on a lore and craft level, Stern's Hobgoblin saga did have an impact, but in terms of actual continuity, actual influence in terms of adaptations and crossovers, Hobgoblin is not a very important character.