The burden of proof is always going to be on the people who make the counter-argument. Initially nobody doubted that Norman was to be the Goblin, then a rumor came that there was a dispute, Lee heard the rumor and having, in his own opinion and Mark Evanier's, a faulty memory, latched on to it. There's no evidence for the veracity of the rumor but plenty of evidence for the veracity of the previous one. So rationally, there's no reason to doubt the truth. Entirely new evidence needs to be offered to defend this.
The big arguments put by people that Ditko was against Norman being the Goblin was that he had issues with a businessman being evil, and that he wanted the person behind the mask to be a nobody for the sake of realism. The problem with the first notion is that Ditko himself, in stories where he had greater control on the plotting, showed Norman as scum. In fact the modern Post-Resurrection Norman is far truer to Ditko's version than Lee-Romita's amnesiac-lame-Dad phase. And in the case of the second notion, Ditko did the nobody behind the mask with the Crime Master. And the third is that Norman wasn't truly known to Peter. The first time Peter and Norman met was in ASM#40, and Peter's first reaction is along the lines of "Of course, you
would be the dad of that douchebag Harry Osborn." He was known to the reader and familiarized with the readers but not with Peter.
Roger Stern in this podcast at Crawlspace after Ditko died in 2018 (
https://player.fm/series/series-2406...er-steve-ditko) also says in response to the rumor when asked about it, that he doesn't believe it. He points out Ditko established Norman as the Goblin, showed him as a shady creep in the stories leading up to that and did the Crime Master thing. Tom DeFalco also interviewed says he has no time for that rumor.