This is an interesting fight, and definitely one that could go in either one’s direction.
New Goblin should scale slightly above his father in physical stats, since his procedure wasn’t interrupted like his father’s was. He’s shown a bit more versatility with the glider itself, such as using the heat it generates as an attack. Harry’s glider comes back to Harry when it senses the rider leaving, and while Green Goblin can control his glider, he has to do so with the controls on his wrist, and I don’t believe it comes automatically like his son’s glider can.
Green Goblin, on the other hand, has used all his equipment to the fullest, New Goblin has used the Razor Bats, Pumpkin Bombs, wrist blades, and a sword to fight, while Green Goblin has used the Razor Bats, Pumpkin Bombs, a trident, built-in knives on his wrists, bullets, and the blades on his glider against Spider-Man, so he has a bit more equipment here. Though Green Goblin should be slightly weaker than his son physically, the gap is clearly rather minimal, since both have been able to fight Spider-Man evenly.
With all this in consideration, I believe I’m going to have to vote for Green Goblin. Though both of them possess most of the same equipment, I believe that Green Goblin is more experienced in using that equipment to its fullest, since he’s used all his weaponry very optimally against Spider-Man. Not to mention Green Goblin is the one who created these weapons in the first place, so he’d probably be more likely to find openings to use them more effectively. Both have their High 8-C missiles, though I’m not sure who would use them first, and even if one of them did use them, the other could just fire their own missiles to cancel the other out. Harry could possibly use his High 8-C heat generated from his glider, though he was only capable of using it against Sandman when he’d grown huge. It would be a lot harder to use it against Green Goblin when he’s flying.
Assuming that both of them use all their weaponry to the fullest and eventually run out of Pumpkin Bombs or Razor Bats to fight, and it would be a battle of hand-to-hand combat, pretty sure Green Goblin would overcome his son. In his fights with Spider-Man, he’s shown impressive acrobatics and been capable of overwhelming both Spider-Men in their bouts, only losing when they became fully enraged and bloodlusted. Meanwhile New Goblin mostly had to rely on his technology in his first battle with Peter, and in their second battle, even if Peter was enhanced by the Symbiote, managed to hold the edge over Harry in close quarters.
Also, though the OP already touched upon it, Harry HAS to be bloodlusted here. If he’s not, then Goblin could take him out easily, manipulate his son into thinking he’s Norman. Green Goblin doesn’t love Harry at all and wouldn’t hesitate to kill him, but Harry would easily hesitate and leave himself opened to be attacked or stabbed just like Goblin tried to do with Spider-Man in the cemetery. Hell, Norman might actually take over: with No Way Home, it gives more evidence that Norman genuinely did take control for a moment when he took off the helmet. But Goblin quickly took over again by manipulating Peter into being like a son to him. That happens to Harry, he’s done for. So both fighters need to be bloodlusted for this match to really work.
