I've read the "stuff". Norman was portrayed as ruthless in the 60's, especially when he framed Mendel Stromm and had him arrested. The lab incident only made his personality worse, ignoring and even gaining hatred for his son Harry, and when he revealed himself to Spidey, there were no signs of double-personality, only Osborn gone from bad to worse. It's not until after this issue that Norman has amnesia from the events, and becomes the "heroic" guy. The ramblings of him trying to be a good father after the first unmasking cannot really be believed, as he was in Goblin mode when he mentioned them.
The split-personality never existed with Norman. It happened to Harry, and it was an invention from the 90's TV series that carried on to the movies and the current comics.
Then I suggest you read them again. Carefully.
So- for you the two issues (ASM #37 & 38) in which Osborn was presented as a ruthless business man equals throughout the 60's??? And even in that story, although unseen, he changes to the Goblin, which is how he shoots Stromm. Ultimately, all of this was nothing but set-up for his being revealed as the Goblin.
Your interpretation is completely off base in that
1. All multiple personalities suffer from amnesia when shifting personas.
2. Norman is never presented as doing anything criminal other than when in Goblin mode aside from framing Stromm. But being shady isn't the same as wanting to take over the world.
3. All of his criminal activities were for no reason but to further his career as the Goblin. He certainly could've been doing the things he's presented as doing now, but that wasn't the character he was developed to be. Prior to his "death" he loved being the Goblin. He enjoyed flying around and blowing things up. That was freedom for him.
In fact, were he the type of megalomaniac he's presented as now, he'd never have become the Goblin in the first place. He'd want the world to see and know that it was Norman Osborn who was in control.
And Harry never suffered from multiple personalities. The only thing he conveniently forgot was Peter's identity. He knew he was the Green Goblin even after being treated, evidenced by his "heroic" appearances as the Goblin in stories such as ASM #180 and 312. So I don't know where you're getting that from.
But in the end, regardless of how you interpret this, Norman's return was ten years after Byrne's revamping of Luthor. And that's how he's being presented.
It isn't as though Marvel hasn't ripped-off DC before- such as when they re-designed The Jackal in Clone Saga 2 to be a green skinned version of the Joker.